The first step is probably to get a better understanding of what the corruption even is. This ether clone technique is still new to you, so it’s not as if you grasp all the finer details of what trouble they can get into.
Well, that’s something of a clue in and of itself. Since it’s such an unusual technique, the corruption is unlikely to be a trap specifically meant for etherform clones. It’s more likely to be a side effect of something else, such as the terror toxin, or something designed to affect etherforms in general.
You don’t think you can guide the others to investigate this, though. It’s going to be some form of advanced magic, perhaps even too advanced to you. But it’s not safe for you to go there, and even if you could protect yourself, bringing this corrupted clone there might make things worse.
Wait. You set up the return command. You set it up to return to the largest ether mass containing some of your consciousness. You could split your main consciousness off into a smaller one.
That’s still dangerous, but it gives you an idea for dealing with one of your other problems. Or rather, something to test. If you split yourself off, and cast the resync spell from the smaller form, would it still mimic the spell? That is, is it mimicking any spell in the area, or just ones from the etherform it’s following? If it’s the latter, you can at least take care of the desync, so it’s worth checking.
You split yourself off, and attempt the spell again, this time carefully watching how the corrupted etherform reacts.
Suggestions:
It is attempting to continue mimicking the last active casting signature from the original etherform it was created from—even after desyncing. And it sucks at it
You feel a slight tug from the corrupted form, like it’s trying to resync with you, but can’t
It begins echoing the version of the spell being cast by your main etherform body, even though that body isn’t casting anything at all.
It’s trying to split itself, but failing
For the desynced one: Try some ether alignment tuning, it’s like tuning a guitar.
Try and replay the moment it got desynced again, check for any clues that way
For the corrupted one:
It tries mimicking every single spell it sees, fails, but starts/learning/ from its mistakes, and it’s getting better at casting