Having this exact issue. Weirdly enough it only seems to be happening to me on my PC, as my wife has been able to play on our PS5 with no issues. I've tried just about everything within my power to resolve this too, from reinstalling drivers to using a VPN, to almost no avail. For what it's worth I'm forced to use wireless since our Access point is locked in a plastic box with a security bolt, but our internet is surprisingly fast for what it is, able to support me and my wife playing at the exact same time, and it was never an issue until last week. We've even played together during this period where I'd suddenly disconnect and she'd be completely fine, able to play all night without running into issues. We ran Tower of Babil together and I dc'd twice while she played through the whole dungeon unscathed, which is so so so strange. I've tested other games too and I don't get the lag or disconnect issues on any other game, JUST FFXIV. Why would it be affecting only my PC, and only one game on it? Gotta be server-side, or some node along the way.
I can't clear the first trial because I always get disconnected before we get over halfway in. It's a really cool trial and I just wanna beat it!!!