pm2 reload not working in "fork" or "fork_mode" with multiple instances

What's going wrong?

pm2 reload is not possible with 'fork_mode'.

//test.config.js

module.exports = {
  apps : [{
          name: "api-dev",
          script: "/home/developer/api-dev/source/dist/src/bin/www.js",
          instances: 4,
          exec_mode: "fork_mode",   //OR "fork"
          instance_var: "PORT",
         //wait_ready: true,
         //max_restarts: 15,
         //autostart: true,
         //restart_delay: 4000,
          watch: false,
         //force: true,
         //max_memory_restart: "2G",
          env: {
              "DEBUG": "test-backend:*",
              "NODE_ENV": "development",
              "GOOGLE_APPLICATION_CREDENTIALS": "XXXXXXXXX",
              "ELASTIC_ID": "XXXXXXXXX",
              "ELASTIC_USERNAME": "XXXXXXXX",
              "ELASTIC_PASSWORD": "XXXXXXXXXX",
              "PORT": 3002,
              "EXPRESS_SESSION_SECRET": "XXXXXXX"
          }
}]
}

I tried every possible fix out there on GitHub or pm2 docs, but as soon as I hit reload command only 1 process starts and other keep on restarting with an error.
It's working with pm2 start..* OR stop && delete && start but I can't always delete and start the process as our deploy pipeline runs 5-10 times a day. Upgraded PM2 to the Latest version 5.3.0 but not fixed.
We want to use fork_mode over cluster because we're using sticky sessions and don't want to change implementations.

How could we reproduce this issue?

pm2 reload test.config.js --only api-dev --update-env

Supporting information

--- PM2 report ----------------------------------------------------------------
Date                 : Mon Apr 03 2023 12:49:55 GMT+0200 (Central European Summer Time)
===============================================================================
--- Daemon -------------------------------------------------
pm2d version         : 5.3.0
node version         : 16.14.0
node path            : /home/developer/.nvm/versions/node/v16.14.0/bin/pm2
argv                 : /home/developer/.nvm/versions/node/v16.14.0/bin/node,/home/developer/.nvm/versions/node/v16.14.0/lib/node_modules/pm2/lib/Daemon.js
argv0                : node
user                 : developer
uid                  : 1000
gid                  : 1000
uptime               : 4087min
===============================================================================
--- CLI ----------------------------------------------------
local pm2            : 5.3.0
node version         : 16.14.0
node path            : /home/developer/.nvm/versions/node/v16.14.0/bin/pm2
argv                 : /home/developer/.nvm/versions/node/v16.14.0/bin/node,/home/developer/.nvm/versions/node/v16.14.0/bin/pm2,report
argv0                : node
user                 : developer
uid                  : 1000
gid                  : 1000
===============================================================================
--- System info --------------------------------------------
arch                 : x64
platform             : linux
type                 : Linux
cpus                 : QEMU Virtual CPU version 2.5+
cpus nb              : 4
freemem              : 6089424896
totalmem             : 8365875200
home                 : /home/developer
===============================================================================
--- PM2 list -----------------------------------------------
┌────┬──────────────────┬─────────────┬─────────┬─────────┬──────────┬────────┬──────┬───────────┬──────────┬──────────┬──────────┬──────────┐
│ id │ name             │ namespace   │ version │ mode    │ pid      │ uptime │ ↺    │ status    │ cpu      │ mem      │ user     │ watching │
├────┼──────────────────┼─────────────┼─────────┼─────────┼──────────┼────────┼──────┼───────────┼──────────┼──────────┼──────────┼──────────┤
│ 81 │ api-dev          │ default     │ 0.0.0   │ fork    │ 20759    │ 22s    │ 6    │ online    │ 0%       │ 292.1mb  │ dev… │ disabled │
│ 82 │ api-dev          │ default     │ 0.0.0   │ fork    │ 21268    │ 3s     │ 8    │ online    │ 100%     │ 156.6mb  │ dev… │ disabled │
│ 83 │ api-dev          │ default     │ 0.0.0   │ fork    │ 21252    │ 3s     │ 3    │ online    │ 100%     │ 161.0mb  │ dev… │ disabled │
│ 0  │ api-staging      │ default     │ 0.0.0   │ fork    │ 31592    │ 20h    │ 2    │ online    │ 0%       │ 120.5mb  │ dev… │ disabled │
└────┴──────────────────┴─────────────┴─────────┴─────────┴──────────┴────────┴──────┴───────────┴──────────┴──────────┴──────────┴──────────┘
Module
┌────┬──────────────────────────────┬───────────────┬──────────┬──────────┬──────┬──────────┬──────────┬──────────┐
│ id │ module                       │ version       │ pid      │ status   │ ↺    │ cpu      │ mem      │ user     │
├────┼──────────────────────────────┼───────────────┼──────────┼──────────┼──────┼──────────┼──────────┼──────────┤
│ 4  │ pm2-logrotate                │ 2.7.0         │ 29577    │ online   │ 0    │ 0%       │ 61.0mb   │ dev… │
└────┴──────────────────────────────┴───────────────┴──────────┴──────────┴──────┴──────────┴──────────┴──────────┘
host metrics | cpu: 54.5% | mem free: 74.1% | eth0: ⇓ 0.002mb/s ⇑ 0.007mb/s | disk: ⇓ 0.096mb/s ⇑ 0mb/s |
[PM2][WARN] Current process list is not synchronized with saved list. Type 'pm2 save' to synchronize.
===============================================================================
--- Daemon logs --------------------------------------------
/home/developer/.pm2/pm2.log last 20 lines:
PM2        | 2023-04-03T12:49:32: PM2 log: Stopping app:api-dev id:83
PM2        | 2023-04-03T12:49:32: PM2 log: pid=20608 msg=process killed
PM2        | 2023-04-03T12:49:32: PM2 log: App [api-dev:82] starting in -fork mode-
PM2        | 2023-04-03T12:49:32: PM2 log: App [api-dev:82] online
PM2        | 2023-04-03T12:49:32: PM2 log: App [api-dev:83] exited with code [0] via signal [SIGINT]
PM2        | 2023-04-03T12:49:32: PM2 log: pid=19670 msg=process killed
PM2        | 2023-04-03T12:49:32: PM2 log: App [api-dev:83] starting in -fork mode-
PM2        | 2023-04-03T12:49:32: PM2 log: App [api-dev:83] online
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:82] exited with code [1] via signal [SIGINT]
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:82] starting in -fork mode-
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:82] online
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:83] exited with code [1] via signal [SIGINT]
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:83] starting in -fork mode-
PM2        | 2023-04-03T12:49:43: PM2 log: App [api-dev:83] online
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:83] exited with code [1] via signal [SIGINT]
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:83] starting in -fork mode-
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:83] online
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:82] exited with code [1] via signal [SIGINT]
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:82] starting in -fork mode-
PM2        | 2023-04-03T12:49:51: PM2 log: App [api-dev:82] online

stackoverflow

Start with test.config.js and reproduce the failure using pm2 reload test.config.js --only api-dev --update-env; inspect the reload behavior for fork mode with four instances and the daemon log output. Done means all configured fork-mode instances reload successfully without entering a restart loop, while preserving the existing sticky-session setup.