On level 45 I realised that my melee damage significantly dropped (from ~110 to ~50 for the Chinese Sword).

My character is focused on melee (10 Strength without any equipment or chems), so I invested into the First League Perk. I suppose the damage drop must have happened when I invested the final fith point into this perk. Unfortunately I can't confirm this, since I do no longer have a previous safe file. I do not use a legendary weapon scaling with armor or comparable figures, nor do I suffer from chem addiction.

Did anyone else experience this damage drop? Is this a bug? If so, Is there a solution?

Thank you very much.

Have you ever worn the Grognak costume or something similar? It increases melee damage significantly I believe.

If it's not that, maybe you accidentally changed the difficulty level? Sorry I can't help you more, I don't use melee very often.

I haven't been wearing that costume and I didn't change the difficulty setting either. It's set on normal, btw.