Sounds like you are not resuing the token.
And you have a misfiring script that is generating/regenerating tokens.
You can have 25 active tokens (per user) and on number 26 it kills access token/refresh token 1.
You should be getting authentication from the broadcaster (in this case you, since you said “your subs”), store that use as needed and refresh every 4 hours (since the normal expire time for a user access token is 4 hours).
So you should be using the refresh token to get a new access token ever 3 1/2 hours or so.
So if your token is dying every 15 minutes, you’ve got something else going on that is killing your token.