Interesting @Wyorp Rock - I've never read about wormer/molting issues. Good to know!
Fenbendazole (Safeguard/Panacur) is the only one I have seen that mentions not to use during molt. There may be others. A lot of people do de-worm during molting since most hens stop laying during this period of time - this way they avoid having to throw away eggs. If a fecal float shows an overload of worms - then of course this would need to be taken into consideration - a molting bird can more easily succumb to worms, parasites and disease since molting seems to make them weaker and treatment may be necessary. Valbazen or Praziquantel may be better choices during motling- but Kathy (@casportpony) would know better than I.
Plumb's Veterinary Drug Handbook says "Do not use during molt (may cause stunted feathers) or while nesting."
@casportpony has a few posts with some links/information here:https://www.backyardchickens.com/threads/fenbendazole-safeguard-panacur-side-effects.1142048/