Quic / http/3 not working in version 1.7.1 directadmin version

Running lsup.sh -e 1.7.7 today to get the updated development release (for a separate caching issue) seems to have re-enabled http/3 & QUIC.
Well, what do you know, today http/3 is gone again. One thing I did was enabling high debug server log and then turning it off.

Another one was adding this to the headers:
Header append Vary Accept env=REQUEST_image
and this to the .htaccess file:
# Pick webp images when available
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_ACCEPT} "image/webp" [or]
RewriteCond %{HTTP_USER_AGENT} "Page Speed"
RewriteCond %{DOCUMENT_ROOT}/$1.webp -f
RewriteRule (.+\.(jpe?g|png))$ $1.webp [T=image/webp,E=REQUEST_image]
RewriteCond %{HTTP_USER_AGENT} iPhone.*Version/(\d{2}).*Safari
RewriteCond %1 >13
RewriteCond %{DOCUMENT_ROOT}/$1.webp -f
RewriteRule (.+\.(jpe?g|png))$ $1.webp [T=image/webp,E=REQUEST_image]
Neither of these things should have any impact on http/3 though.
It came back after I stopped lsws, killed all lsphp processes, and restarted lsws. Will probably go away again at some point. At least that has been my experience. Works after restart only for a while.