Now my ad doesn't show up for almost any combination plus keyword.
Ditto for most competitors. There is only 1 (one) ad showing for most combinations with a keyword from this group.
Something similar happens in some other groups, but some other groups are fine. It's not a budget matter.
What could be wrong? Too many exclusions? How many is OK then?
I think you'd get a much more solid answer by contacting AdWords support using the 'Contact Us' link from within your account.
One thing that immediately came to mind though: have you made certain that your campaign level negatives are not preventing some of your keywords from showing?
Too many exclusions? How many is OK then?
I don't think this will be the problem - and least not in terms of simple numbers. I'm not aware of a limit to the number of negative keywords which one may use.
AWA