Maybe it's a campaign problem, because if it's an ip or credit card problem, it's immediately suspended,but the account was only suspended after the campaign was created
Not necessarily that way (as you mentioned).
Let's say you created the GAds account, added payment method, then created campaign and then account suspended (suspicious payment), it can STILL be due to bad account creation method. Or, it can in the same case be suspended due to improper campaign (niche, improper campaign setup, etc).
And 1 more thing : Suspicious payment suspension also happens due to improper campaign (niche, improper campaign setup, etc). 1 example of the DOZENS in this scenario : one creates a 100% safe campaign (allowed niche, proper campaign setup) BUT high daily budget, nowadays account will get suspended showing as due to suspicious payment, whereas the actual reason has nothing to do with payment (card, etc).
What you have to do is experimentations to narrow down to the cause of your GAds account suspensions.
However, nowadays from what I've been seeing is that people are getting accounts suspended due to improper account creation method : they are creating GAds accounts like how things were before a year ago. People do not realize that GAds overall algorithms and GAds review algorithms are now beefed up and hence account creation method also needs to match up.
One needs to think that one is the GAds review bot (or algorithm) : what all would it look out for ? All the answers are there.