Hypothyroidism symptoms can occur with normal TSH if T4 is preferentially shunted into reverse T3 instead of T3.

“you can sometimes have a normal TSH and still have the symptoms of hypothyroidism if for example you have very high amounts of reverse T3 and very low amounts of T3 in other words if your T4 is being preferentially shunted into reverse T3 instead of T3 you might feel like you have the symptoms of hypothyroidism you could be cold your metabolism might be slow you'd have difficulty sleeping if it were really extreme your nails might even get brittle you'd be constipated these sorts of unfortunately non-specific symptoms which make it difficult to make such a diagnosis at times”