What i did / Steps to reproduce

Installed bluemap, set it up for all maps, preloaded chunks with chunky and rendered tons of chunks.

Expected result

webapp should load "instantly" without errors.

Actual result

524 error(timeout), loading issues like blackscreen and nothing is happening until another reload, endless loading for some reason.

Context

BlueMap Version:
BlueMap-1.5.5-spigot

Optional:
There are no errors, no low tps/performance issues, just the fact that it doesnt load correctly.
Using latest paper build(git-Paper-71), also installed Bluemap skins, townyblue and bluemap essentials.
Host machine: dedicated server, 6 cores @ 3,9ghz boost up to 4,2ghz, 64gb ram(up to 16gb useable for mc server), only nvme ssd storage, server is running in a docker container. Container never had such connection issues. Connection to the map gets redirected with a apache2.4 proxypass:

ServerName map.servername.eu
ProxyPass / http://127.0.0.1:8123/
ProxyPassReverse / http://127.0.0.1:8123/

TCP port is forwarded and working, i used dynmap before but its uninstalled now.

Thanks for help, i hope thats enough information for you.

I am not happy with Undertow, so i am dropping this idea for now.
I found an issue that might have caused this issue and fixed that.
The next version (>= 1.6.1) will include this fix.

Seem to work fine with external webserver, maybe an issue with the internal one?

Seems to be something happening rarely on some setups. I can not reproduce this on my end, but similar problems have been reported by 2 people until now.
This happens since 1.5.x

I'll probably replace the (self written) internal webserver entirely with Undertow. That should then fix this.