Weird server side lag/speed issue

Some maps randomly slow down and quicken server tick intermittently.
* Both CPU and GPU process frame sub 5ms, no local lag or extensive resource consumption
* Ping does occasionally jump but not in excess of 250ms
* Most of the time the game runs at about 5-6 server ticks per second. The game remains responsive and local FPS is stable in this state, but it feels like trying to move through molasses.
* Afterwards the instance randomly hastens to 2-4x the speed to "catch up", either replaying previous input or ignoring it completely until the burst of speed ends, usually in character death. If the character survives, the instance runs at regular speed for a couple of seconds before slowing down again.

I can't determine if it's a specific mob, modifier or league mechanic.

This has already happened many times in maps, and I recall this happening once or twice in the campaign too. It is very annoying and usually results in losing that map.

Had this too an hour or so ago in a Gardens map containing a breach hive and a harvest. There was minimal lag when moving the character with nothing much going on, but it seemed to scale up with the number of mobs and abilities being used. No issues with any other maps prior to that one today.

I know you don't believe this to be a connection-related issue, but an MTR log created while you're observing such speed variances could still really help GGG investigate this.

https://www.poecommunity.help/information/server-connection

That seems sporadic and affects only different instance/servers.

Modem restarted, no issue whatsoever on any website/ping anywhere else, worked one map after restart, then the next map, once again clown fiesta.

Having layers of RNG on top of RNG is definitely a signature move from GGG for years now.

Same issue here fast forwarding in x4 speed / x10 speed after playing in slow motion for a while not sure what is triggering it :(

switched to london but the issue came back there also :(

Paused the game for 1min in a laggy map and it seemed to have fixed it for that map.

Same issue here, there were no such issue before yesterday.
Did 2 breach dune maps (literally unplayable) and some pinnacle bosses. And it become pretty sure it's not my computer, when I experienced this lagging on uber shaper and elder too after 3-4 minutes of normal gameplay... there is something seriously wrong