Relighting causing extreme memory/CPU usage

Server Implementation

Spigot

Server Version

1.21.10

Describe the bug

Upon copy/pasting a lighting block (and perhaps also a lighting-affected block such as a block inside a lighting glitch?), the relighter draws huge memory usage, eventually leading to high CPU usage as garbage-collection struggles to keep up, and eventually a non-functioning server.

Relogging will in some instances cancel the relighting job, effectively fixing the bug, but also leaves large areas of broken lighting that can lead to further instances of the bug (it would seem). In at least one case, subsequently logging on and trying to use WorldEdit commands resulted in a job cancellation due to low memory, despite memory being available.

To Reproduce

1. Start with blank server, just FAWE.
2. Log in, place a glowstone block.
3. //copy the glowstone block.
4. Move to a new position, use //paste.
5. Kaboom.

Expected behaviour

I expected the server to remain healthy ;)

Screenshots / Videos

https://xorg.us/idea64_2025-11-17_01-34-54.mp4

Error log (if applicable)

No response

Fawe Debugpaste

https://athion.net/ISPaster/paste/view/255ba270af8c4a90a7515c9527c2bda7

Fawe Version

FastAsyncWorldEdit version 2.14.1-SNAPSHOT-1214+6205e5c

Checklist

• I have included a Fawe debugpaste.
• I am using the newest build from https://ci.athion.net/job/FastAsyncWorldEdit/ and the issue still persists.

Anything else?

No response

Start by reproducing the issue with a blank Spigot 1.21.10 server, FAWE, and the glowstone copy/paste steps. Inspect the linked FAWE debugpaste and observe the relighting job's memory and CPU behavior; done means the paste completes without runaway resource usage or leaving broken lighting.