Hello and welcome – I’ve not heard of a connection specifically with IVF, but the post-pregnancy period is a very common time for Graves’ disease (as well as other issues affecting the thyroid and other autoimmune diseases) to surface.
Untreated hyperthyroidism or hypothyroidism increases the risk for miscarriage, but I haven’t heard of miscarriage itself affecting previously normal thyroid levels.
Hopefully, others here will chime in with their experiences as well.