12 subscriptions are too few. I set it to 50 on my relay, because it seems that some clients will use more subscriptions. If it is below this number, there will sometimes be an error message.
Discussion
I thought you were talking about the number of subscriptions. I misunderstood.
But bigger number of subscriptions also help... I had to mix unrelated filters into given subscriptions just to avoid the 10 sub limit some relays have.
Have you seen Amethyst hitting your relay limits?
I think the different settings of each relay will indeed bring difficulties to the client. Similarly, relay operators also spend a lot of time to investigate and adjust in order to support different clients. I saw the problem of exceeding the limit before, but I just changed the settings, I haven‘t seen what the client is.
I’m testing some clients on iOS now. I haven‘t had time to see Amethests yet. Is the subscription ID a 4 character string? I noticed that the requests for this kind of subscription number are quite frequent.