The latest member of my S2Member membership site cannot access her account.
She gets a 503 Service Temporarily Unavailable error message and the statement “Too many IP addresses accessing one secure area”.
Also another member was unable to change their password by themselves.
I’ve checked with my hosting account and they say it isn’t a WordPress or database issue.
Is this an S2Member issue?
First, check the s2Member => Restriction Options => Unique IP Address Restrictions settings. Sounds like you might have them pretty tightly restricted. Then you can clear the IP address info for a single user (this user) as shown in this KBA: https://s2member.com/kb-article/how-do-i-reset-ip-restrictions-for-a-single-user/.
What Pat said about the IP restriction.
Maybe you have the default value for that setting, which is fine for most, but that particular user may be connecting from several places, or even has an internet service that keeps changing his address and ended up being too many.
So you can reset his IP restriction and adjust the restriction to be less strict.
That’s a WordPress thing, it’s not handled by s2Member. 