What Annie says: it's not MG causing thyroid issues, but the other way around is very possible.
They sometimes come together in the same patient because thyroidproblems are often auto immune diseases, like AchR MG is. And thyroid auto immune diseases are quite common.

There are some things that make it more difficult; like some people with auto immune thyroid diseases can be false positive for some antibodies (they show up but you don't actually have the disease). And, thyroid issues can cause problems like weakness and eye issues, it's sometimes very hard to know what is really going on.

Do I understand correctly you do not have a MG diagnosis?

I, for example, have Hashimoto's disease: hypothyroid. I've had this for 5 years, 2 years under control, before my MG symptoms started (so, 11 years now). When my first MG problems started, my thyroid was still between range; so my thyroid bloodwork didn't show anything wrong with my body at the mo,

Been hyperthyroid once while having MG, and it caused a very significant MG flare up. The other way around never happened with me; had many MG flare ups, but none had an effect on the thyroid (thank God!).

Still have the thyroid antibodies, but I take the same thyroxin dosage for years now.

Hope the lower dosage helps, good luck,