I've run into similar issue with the Odyssey 2 core and can somewhat replicate it.
I believe this may be an issue related to savestates.
Using the Pinball ROM, I can show some images to explain a bit of what I'm encountering.
When I just load the ROM, open TAStudio and start running emulation; I get the following:
When I add input, the following occurs and I get the wall of lag:
Then after the input is in place, restarting emulation from the beginning will result in this:
Then sometimes (but not always), clicking to jump back the emulation at an earlier frame results in the big block of lag returning. In this example I clicked to jump back to frame 12:
I'm not sure if this is the same bug that Lobsterzelda is experiencing, but it sounds related.
Again, I'm guessing it's a savestate issue, but I'm not a coder to know how to investigate further. There are no error boxes/logs/reports occurring.