The thyroid "warning" is based on ONE study on animals only.
It used only ALPHA racemic ALA and not the purified R-lipoic.
So the other portion of the racemic version may be the culprit, but no one knows.

It has never been done on humans or replicated. Replication by other study groups is typically needed before concrete
conclusions can be brought on medical issues.

When any "negative" thing appears in searches of MedLine, all the quality online sites pick it up and repeat it. In this case it has not been proven at all at this time and not in humans.

People on thyroid treatments, should be monitored anyway carefully for changes. So any effects would show up that way.

I am hypo and I take R-lipoic and have noticed no new signs of my hypo that I suffered with before I was diagnosed. In fact my cold intolerance is better!

It is your choice in the end, but consider the decision is based on very little evidence.

I'd take the gabapentin by itself spaced a long way time wise from any mineral supplement. Magnesium is ++ (called divalent) like calcium and iron are and it has shown to reduce gabapentin's absorption in the GI tract. Gabapentin is already not well absorbed under ideal conditions.

Fiber is well known to complex out some drugs. Fiber will prevent thyroid hormone from being absorbed at all!
I would space out fiber as well, away from gabapentin AND thyroid replacement hormones.