Apart from what I already told you about coinos, I will add something else. All the communication of a coinos with SN account is through NWC. We know that. OK good, NWC works with nostr relays. These nostr relays sometimes can have a lot of activity and could limit the whole number of items passing through, depending on how they are configured.

Also they can limit the access to specific IPs... I had a stupid issue with Rizful node testing. I contacted the admin and he told me they had some limiting access to some IPs so I changed my NWC access to another IP and all worked flawlessly (I was zaping on nostr from a restricted IP and Rizful relay couldn't fw the payment).

btw... primal is restricting heavily to connect to many relays other then theirs... so all your zaps could fail.

So yes shit like this can happen and IS NOT SN fault !