Currently I’m facing an error that already occured in some particular cases in the past, too. The undo function doesn’t work for whatever reason. I didn’t do anything special, just business as usual, which means loading a few samples and VSTs, editing a few notes, applying a couple of devices to the tracks and so on. And there’s absolutely nothing that can be undone. No note editing, no parameter settings of devices, no instrument load or whatever, simply nothing. Undo and redo are always greyed out. This error is only happening in that particular song, and in contrary to that undo works normally as expected in other songs. Obviously this isn’t a bug in general, it’s just weird and not comprehensible for me. I think this is the third song in which I’m facing this error. It’s definitely not happening because of a crash or somehing like that, it just happens out of the blue. Btw, I’m on Win10 and I’m currently using Renoise 3.4.3, but this error also occured in particular songs that were made with previous Renoise versions.
So my question is: What could cause undo not to work?
Could a tool influence undo behavior? What if you disable all your tools in the tool browser and test the particular song again, does the problem persist?
Thanks for diving in. 
Nevermind, I think I’ve found the culprit. Seemingly this error is caused by a VST instrument. In this case it’s ProtoPlasm. As soon as I delete it from the instrument list, undo and redo are working again. I just don’t get it, because usually that VST doesn’t cause that kind of error. I guess it has something to do with some settings in terms of the particular instrument that I’m using.
It’s definitely neither caused by any setting in Renoise nor by a tool. The only two tools that I’ve got installed are “Place Selected Notes Evenly” and “Native DSP Context Menu”. If the error occurs, it always looks like that:
Protoplasm 
Unfortunately, Protoplasm and the rest of HG Fortune’s synths that I’ve tested break Renoise’s undo function. When I ran into that issue I read somewhere the problems might be related due to it being an ancient synthedit synth.
They are however wonderful synths! So I went looking for the maker’s contact info, to see if he would be willing to share the original samples. But turns out that he had died already by then. So I started to re-sample Protoplasm’s samples. To recreate it sounds natively in Renoise. Still need to finish that project one day.
Maybe someone with more skills than I have can actually brake open the DLL and extract the audio files?
It is available here for free, for example, if anyone wants to have a go:
Here are the first 38 out of 128 samples from Protoplasm. These are all 35 seconds long and not yet looped. But it’ll allow you to recreate some of the Protoplasm presets inside Renoise’s sampler.
Thanks for the samples! Personally I still prefer the VSTs.
That’s interesting, thanks for the hint. From the day that I started using VSTs I’ve got all the VSTs by H.G. Fortune, and until today I’m using some of them now and then despite the fact that they’re sample based and therefore limited, but I’ve never noticed that kind of problem in connection with those VSTs. And especially at the beginning of my “Renoise career” I used them a lot. So I just have checked a couple of them and indeed there are a few that cause undo not to work. But not everything by H.G. Fortune causes this, some STS ones for example don’t. I gotta check some old songs, just out of curiosity. I’m sure some years ago there wasn’t any “undo issue”, especially not like 10 years ago…
Windows is bugged like WTF, upgrade to WIndows 12 now.
More seriously, is ProtoPlasm running in bridge mode? Did you disable it completely? Curious…
Jup, still running with JBridge. Even though I’ve heard it’s not necessary in Renoise (anymore?).
Do you think disabling JBridge would fix the issue in terms of undo? What about you, @eretsua ? Are you using JBridge or any other brdge, or have you checked H.G. Fortune’s synths without bridging?
yes, I imagine that. Just use native x64, disable bridging completely. Also latency will be better.
Can you run a 32bit plugin in 64bit Renoise without bridge mode?
My sandboxes are turned off. But I always assumed it would turn itself on to run 32bit stuff. Maybe I’m wrong?
Anyway, no change if I enable that. Undo keeps saying it has nothing to do.
IIRC, this issue started to appear with version 3.0 or 3.1. Don’t remember exactly.
Yes as soon as you use 32 bit plugin in 64bit Renoise, the bridge will be used, no matter what. Maybe try with 32 bit Renoise version…? Or just replace that rusty plugin. Or simply buy a Mac Pro.
Makes sense, but I would recommend buying a Macbook Air…
I just have checked and according to that post by taktik no external bridge is required in Renoise. Damn, that comment is 12 years old. It seems JBridge wasn’t necessary since then.
it seems I was mistaken and JBridge is not active on my “new” computer that I got 2 years ago. I was irritated by the fact that there’s still the “(–> 32bit)” in the window title, and before bridging with JBridge that was never the case. Currently it still looks like that:
Anyway, I just have reinstalled ProtoPlasm again and just like @eretsua already mentioned there’s no change. Undo is still not working if ProtoPlams is loaded. So one have to live with it.