I have checked into this and there is a reply limit on your first day as a newbie to the forum.
It doesn’t matter if you move from the New User to Basic User trust access level. It’s a built in feature to reduce SPAM.
I’ll update the guidance on the Forum User Access Levels
[Edit: Guidance now updated. Also a way around this can be to PM as you have already mentioned (as long as you have Basic User access and not New User as this is restricted), or to edit a previous response]