Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.30813.1> exit with reason normal in context child_terminated

Seeing the following messages repeatedly in /var/log/couchdb/couchdb.log:

[error] 2018-11-14T15:54:51.599025Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.4622.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:54:56.606364Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.4775.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:01.614952Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.4886.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:06.622537Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5031.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:11.631585Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5141.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:16.638075Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5284.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:21.645321Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5396.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:26.652175Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5537.2> exit with reason normal in context child_terminated
[error] 2018-11-14T15:55:31.658958Z couchdb@127.0.0.1 <0.419.0> -------- Supervisor couch_peruser_sup had child couch_peruser started with couch_peruser:start_link() at <0.5647.2> exit with reason normal in context child_terminated

## Expected Behavior

No error messages.

## Current Behavior

Many error messages and beam.smp memory usage gradually rises until it crashes.

Otherwise, no visible issues with CouchDB installation.

## Possible Solution

## Steps to Reproduce (for bugs)

1. Occurs even whilst CouchDB is idle
2.
3.
4.

## Context

Happy to provide more information.

## Your Environment

* Version used: 2.2.0
* Browser Name and version:
* Operating System and version (desktop or mobile): Ubuntu 16.04.4 x64 runing at Digital Ocean with 1 GB Memory / 25 GB Disk
* Link to your project:

Start by tracing the couch_peruser_sup supervisor and couch_peruser:start_link() entry point mentioned in the repeated log messages. Reproduce the behavior while CouchDB is idle and determine why the child repeatedly exits normally and memory usage rises; done means the messages stop and beam.smp no longer grows until a crash.

Written by the indexing model from the issue text.