I finished this game last night. Learned a few things that I will need to take forward.
First, I had a challenge to finish the game, as noted in this thread
https://forums.civfanatics.com/threads/late-game-crash-turn-337.676528/ My victory was still ~18 turns away on turn 336, when the game crashed. Lately I have been not hurrying to victory, since the scoring system gives no bonus for finishing quickly. I wanted this game (as Kozlov) to score higher than my last game with him.
Recovery Plans: I remembered making a conscious decision to pursue some Supremacy techs on the way to finishing the 3 required techs for a Harmony victory. Clearly, to avoid the crash at turn 336, I would need to finish my Mind Flower sooner so that it could connect before turn 336. I tried going back to a save from turn ~280, but the tech decisions were still baked in at that point. I went all the way back to a save from turn 215 or so, where I could beeline to the required Harmony techs.
Accelerating City Improvements: Elsewhere in the strategy forum, I had read that the improvements need to be finished *before* the Mind Flower is completed. I can confirm that. I can also confirm that a Mind Stem that finishes *on the same turn* as the Mind Flower doesn't help. By playing to beeline the Harmony techs, I started the Mind Flower earlier and it finished building just before turn 300. It required 36 turns to connect, so I was sweating whether the crash would still occur.
AI Changes: In the previous attempt (that crashed on turn 336), the objectors had been PAC (my immediate neighbor to the north, on the same land mass) and INTEGR (on the other big land mass). This time, as I started the Mind Flower, the objectors were PAC and ARC. That was good news, in a way, because ARC was somewhat weaker at that point. Fielding was still pursuing a Contact victory, making significant progress on Decode Signal at that point. She would go on to start building the Beacon.
ARC had a fast start, wiping out Polystralia with her navy. ARC was located in the southern hemisphere, with a clear ocean path to Polystralia's cities. She overextended herself attacking NSA (neighbor to the west, accessible through a southern ocean passage. Where before PAU had been poaching a few INTEGR cities and keeping Lena in check, this time through INTEGR built up an army. Took over ARC's conquests in the former Polystralia (far to the east of INTEGR) and later swept down to take out NSA in the south.
AI Victories -- Human Saved by Stupidity: As I worked to build my Mind Flower as quickly as I could, two AI nearly beat me to the finish line.
PAC Supremacy: Daoming had been steadfastly building her affinity level and her army. Lots of skirmishes with Africa and INTEGR in the northern ocean passages, but also settling a bunch of cities. She gets to affinity 15, builds the gate, and ... puts it in the water. I made this mistake in a previous attempt with Supremacy using NSA; all land units are embarked when they go through, so their strength is reduced. When she declared on me (as my Mind Flower waited for connection), I took a while to get troops and planes into position to attack the gate. She pushed through ~300 points worth of troops before I could mount a serious threat. Lesson 1 in complacency by the human player.
INTEGR Harmony: As I noted in the first post, Lena had teched all the way to level 14 in Purity, while seeming to have a change of heart to pursue Harmony. She had amassed quite an empire with multiple cities and lots of land. She made it to level 15 level in Harmony and built her Mind Flower in a size 23 city that was NOT her capital. A bit too late; she finished her Mind Flower while mine still had 10 turns to go before connecting. According to the victory log, her MF would have needed the whole 40 turns to connect. Did not appear to have built any accelerating buildings in time.
I like looking at the "replays" in the game main menu, just to see how I did compared with the other AI. I was out-teching and out-producing PAC, but INTEGR crushed me in score, tech, productivity, even military might. Lesson 2 in complacency by the human player... I should have intervened to slow her progress. When the AI gets a good start, on another land mass, they have the potential to run away. Her empire was strong enough to support two victory conditions at nearly the same time -- like mine have been in previous games.