Is this related to how fast you call updateServices?
Yes but with more testing I've seen it failing even with first call. It looks random, probably depends on timing in bluetooth stack -whether it is currently possible to send data or not.
It is also discussed here (there may be some queue size to tune)
https://devzone.nordicsemi.com/f/nordic-q-a/66265/ble_nus_data_send-is-returning-nrf_error_resources but still, with or without tuning, we should not ignore errors there
I don't think this will probably affect me because I plan on polling the characteristic anyway but getting notifications would be much better so data can be sent automatically. Is this related to how fast you call updateServices?
@Gordon have you experienced this problem