Don't know for sure but sometimes it seems the seal gets deformed and just won't seal again. I prefer to just replace them if I have to disconnect the toilet, it saves lost time in labour refitting and re-checking.
It's not always effective but a bit of lsx sometimes is enough to seal a small drip.
Easy to underestimate the pressure that builds up on that joint for a second or two when the toilet is flushed. It's not always enough to rotate them. Are you sure the angle hasn't changed.
Don't know for sure but sometimes it seems the seal gets deformed and just won't seal again. I prefer to just replace them if I have to disconnect the toilet, it saves lost time in labour refitting and re-checking.