Try a couple of things.

1) Get a roll of different film. Expose and process.

2) Expose a roll of the Agfa then send it out for processing.

If it's the film then the first one should be good the second one bad. If it's you then the first one will be bad the second one good.

Supposedly a carbonate developer can cause problems with stop bath but I thought all modern films were hard enough to handle it.