Hi,
I use nrf52832 with SO 6.0.0 and SDK 15 connected with and IOS 14.2 (iphone XSmax)
some time (about 1 time on 400 connection) in the first packets exchanged after connection the device (nrF52) send on the ATT protocol the MTU information but the IOS do not send back the answer.
in the picture below the first section there is a tipical good connection where in the packet 5579 and 5580 the device and the IOS exchange the packet size and after that, more later, the phone sends a command (write Request) and the nrF52 send the ACK with flag more data = 1 and after send the answer.
in the second section there is a "bad connection" in the packet 33343 the nrF52 send to the IOS your maximum MTU (247) but the IOS do not send back the answer.
In this situation the connection START but when the IOS send a command (on write Request) packet 33496 the nrF52 send back the ACK with flag more data = 0 and do not send back the answer)
Have you any idea where is the problem ? Is in the phone ?
with android this situation do not append
best regards
Marco