I quite often use emacs as server on my desktop computer and connect to it via ssh forwarding from my laptop.
So far it works very good.
But after last update (emacs27) every time when server lost connection to client emacs exits (and is restarted as systemd service)
below example log

2020-11-13T17:18:47.010288+01:00 alfa emacs[2074314]: Debugger entered--Lisp error: (error "Connection lost to X server 'localhost:20.0'")
[..]
2020-11-13T17:18:48.051958+01:00 alfa systemd[2825]: emacs.service: Main process exited, code=exited, status=255/EXCEPTION
2020-11-13T17:18:48.052214+01:00 alfa systemd[2825]: emacs.service: Failed with result 'exit-code'.
2020-11-13T17:18:48.298927+01:00 alfa systemd[2825]: emacs.service: Scheduled restart job, restart counter is at 2.
[...]
2020-11-13T17:18:54.769108+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/00debian.el (source)...
2020-11-13T17:18:54.769413+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/00debian.el (source)...done
2020-11-13T17:18:54.831855+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/20apel.el (source)...
2020-11-13T17:18:54.894324+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/20apel.el (source)...done
2020-11-13T17:18:54.906380+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/50auctex.el (source)...
2020-11-13T17:18:54.906559+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/50auctex.el (source)...done
2020-11-13T17:18:54.916376+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/50autoconf.el (source)...
2020-11-13T17:18:54.916548+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/50autoconf.el (source)...done
2020-11-13T17:18:54.923012+01:00 alfa emacs[2191157]: Loading /etc/emacs/site-start.d/50dictionaries-common.el (source)...
[...]
2020-11-13T17:19:51.914470+01:00 alfa emacs[2191157]: Wrote /home/kjonca/.emacs.desktop.lock
2020-11-13T17:19:51.914635+01:00 alfa emacs[2191157]: Desktop: 1 frame, 183 buffers restored, 3 failed to restore.
2020-11-13T17:19:51.914694+01:00 alfa emacs[2191157]: Starting Emacs daemon.
2020-11-13T17:19:51.920942+01:00 alfa emacs[2191157]: Restarting server

I tried to install emacs-lucid:amd64=1:26.1+1-3.2+deb10u1 and effect was the same, so this behaviour does not depen on emacs version.  Maybe some additional files were changed?

KJ

Seems that it is related to debug-on-error variable.
When it is set to non-nil - emacs exists with error.
When it is set to nil - emacs survives lost connection.
KJ