Guardian article which, though strictly speaking could be off-topic, is nonetheless of possible interest and relevance.
I wonder if failure to restore thyroid hormone levels adequately could be a contributory factor - at least for some?
Long Covid: what we know so far
Lasting symptoms may not be down to a single syndrome but several different ones
theguardian.com/world/2020/...
That, in turn, follows another issue that has recently been reported:
Covid may cause sudden, permanent hearing loss – UK study
Study team says Covid-19 patients in intensive care should be asked about hearing loss