During combat, some instances freeze, requiring me to log out: "infinite latency spike"

On some endgame map instances, when I am in combat, gameplay will freeze and the latency counter will keep incrementing indefinitely. This does not happen in campaign/interlude. Only endgame maps. I've given it several minutes and the game never unfreezes. However the program itself is not frozen as I can return to login screen, only gameplay is frozen.

Returning to the login screen, and logging in to play the same character works. I can continue on the same instance, until the same thing happens again. I have tried playing through an entire map this way. It can happen dozens of times and how frequent is not predictable, sometimes minutes apart, sometimes only seconds.

It seems to be worse on corrupted maps, but I have confirmed it is not only corrupted maps.

Note that this does not seem to happen out of combat. It's specifically only in combat that I've experienced this. To test I have spent a while (minutes) unpaused out of combat, just standing in the instance and it doesn't seem to freeze. (Edit to add: I just cleared a map to 0 monsters remaining, and have spent 10+ minutes sitting in it, no freezes!)

I can't isolate a specific aspect of combat, but it might have to do with offscreen enemies? Hard to tell.

Note also that this does not happen on every instance, only some instances. Once it happens once on an instance, it's a guarantee that it will happen many times. It feels instance-specific.

This is not a network latency issue as my latency can remain stable without any spikes and this will happen. As far as I can tell this is not a client issue. Resource usage is normal throughout.

This was an issue the first couple weekends of the game. Since then this issue has gone away entirely. Probably something like a server load issue.