Interesting. It taking that long - you mentioned five minutes! - still seems to indicate that there's something going on to slow it down, though. It's possible that the leak just isn't quite big enough to make it crash while saving but just big enough to make it slow, but, yeah, that'd be a fine line for it to walk. The really low campaign framerate seems to be almost be more indicative of some kind of cumulative problem with, say, the same script getting repeatedly added to the game or something that just over time adds up and massively slows it down.
Semi-related note: how big are your savefiles? The size of the campaign.xml, specifically.
My lategame saves are well above 70MB, with my current one being roughly 82MB and climbing. I haven't had the time to start a new game yet to hunt for "that" behavior again, but there's a weekend approaching.
As for the fine line: I deliberately tried to
keep going to see if I could eventually reach a GC crash. Yet even when the game slowed down to a crawl, no crash occurred. Additionally, since these performance drops were not in a smooth curve but more like falling down a flight of stairs, I usually had one big fight, maybe two if I felt masochistic, then I saved and restarted the game, plus clearing out my RAM standby list. Repeat this process in 2h to 3h intervals, depending on what I was doing - exploration without fights usually went well enough. But it never crashed on me, no matter how bad I let it get.
As these problems became a steady and constant issue, I made a save I declared my "last", and set sail for crash country. And yet, I never found the shores. The worst I found was the aforementioned ~3FPS and the ~5 minute saving of a game (time measured by the highly academic method of clicking
Save & Exit, then getting water, going for a smoke, and coming back to watch the tail end of the bar fill up. The margin of error is 2 minutes). Then I posted here, set up VisualVM as instructed, and was ready to bug hunt like a pro. I picked a war with every neighbor I head, smashed into three IBBs, two HVBs, made Sylphon RnD homeless (Sorry, Nia. ;_;) and finally rolled into a High Danger Bladebreaker system, killing off battlegroups three at a time with a 300 DP battlesize - and Bladebreakers don't retreat.
The
battles slowed down and stuttered over fighter spam and particle hooray. But as soon as the battles were over and the loot looted, the game returned to an almost normal state. It
was slightly impacted, but nothing that'd make me consider the Restart Dance. It kept on chugging. I have nothing in my hands but questions.
The only thing I did between my first post in this thread and my VisualVM setup was installing JDK 14.0.3 - same mods, same vmparams RAM settings, same save file.