MIDI and audio latency 12.5.11

[squirmish]

Over the past year and earlier I had been able to record guitar through plugins with no latency issues, in fact without having even considered any related settings. I had a break from recording for a few months, just editing and mixing stuff. Now I've come back to wanting to record with the same setup and I'm getting awful latency issues - both with audio inputs and midi. I want to have live guitar fx for an upcoming performance, adding to where in the past I've successfully played keyboard-triggered synth VSTIs. Currently I'm getting latency in the hundreds of ms.
I'm using the Behringer UCA222 for my live setup, but I'm getting the same issues when using the Focusrite 18i20.
Using the UCA222 the ASIO4ALL buffer is 512/11.6 ms.
I set the buffer to 512 as @peterwiddicombe suggested this worked well in a post a couple of years back. And of course I've got live input monitoring enabled, track o/p is 1&2.
I'm preparing to reset my laptop and have been backing up everything that's on the C drive, in case it comes to that.
All of the above is running on version 12.5.11, which I believe was what was running previously. So as a last chance I thought maybe reinstalling might fix it, so uninstalled ver 12. Then I noticed I still had ver 10 onboard, so I booted that up.
NO issues, same settings.
Reinstalled ver 12. Same issues remain.
Anyone have any clue as to what's going on here?

[squirmish]

Bah, I forgot to include that I'm using the Roland UM-One as midi interface.

[dysjoint]

Is it the same with all plugins disabled?

[squirmish]

Just to clarify - @dysjoint: it *was* the same with plugins disabled, as I was initially just looking at signal flow, however, as you can see above things have moved on. But they got weirder too. The next day after all the above, v12 worked as per v10! So I did a comparison of all the settings of v10 and v12 - I'd only compared the audio device settings initially. Everything was the same, except of course there are a few more parameters in the v12 Advanced settings - that menu menu is missing in v10.
(And a correction to my original post: last time I performed using the UM-One it was v10, not v12.)
And then today it's gone weird again. V12: I have a project on my C drive with 2 edits - one for each performance unit I'm part of. I've set them up identically as far as inputs, plugins and track outputs go. One works perfectly, the other has both the original latency issue for midi and for audio I can see it at input but at track output I can see the delay on the meter (plugin disabled), but additionally that doesn't get to the master output.
Another strangeness is this: in my midi track I have a Reaktor synth loaded. In common with NI synths it has animation which moves whether you're playing or not. In the problematic edit it sits there as if it's empty, and doesn't respond.
Back in v10, no problems. I'm *kind of* OK with the idea of just using v10, but managing the two versions is fraught with the danger of accidentally opening a v10 edit while I have v12 open, then being unable to open it again in v10.

[squirmish]

So ... I haven't been back yet and actually tested this theory on what was happening, but just looking again at my experience I believe this is it: in my live gig project with the two edits, I can now confirm that the one misbehaving was definitely created under v10, the well-behaved one under v12. Seems v10 can handle the input processing for v10-created edits but v12 can only handle v12-created edits. If that's correct, TSC need to give more of a heads-up when opening old projects than the belated 'This edit could not be loaded because it was saved by a later version of WF' that you sometimes get.
Please discuss.

[talby]

Just to understand you correctly: So, at least when you made the completly new Edit with V12, then this works with the desired low latency?

[squirmish]

Yes. Apologies for the lack of clarity - it was a difficult scenario to put into words!