I wouldn’t assume anything here. Rather, use maximumDatagramSize to see if your packet will fit. I'm a little confused about the number being returned here. As I send each frame, the majority are going through despite being significantly larger than this number. Here's a log where I log the data count I'm sending vs maximumDatagramSize. Only when there's a spike does the frame freeze and I see that error message. Sending size: 15344 - maximumDatagramSize reported: 1472 Sending size: 18182 - maximumDatagramSize reported: 1472 Sending size: 17145 - maximumDatagramSize reported: 1472 Sending size: 14539 - maximumDatagramSize reported: 1472 Sending size: 16288 - maximumDatagramSize reported: 1472 Sending size: 19660 - maximumDatagramSize reported: 1472 Sending size: 25691 - maximumDatagramSize reported: 1472 Sending size: 52437 - maximumDatagramSize reported: 1472 2021-05-24 08:49:08.983732-0400 App Name [23702:7182702] [] nw_protocol_ipv4_frame_output_finalizer [C3:2] Not enough bytes to fragment 52445 I'm unable to find any information on that particular error message and although I see it in the console, there is no NWError in the completion block of connection.send.

If you're desperate, try unchecking "Include bitcode for iOS content" and "Upload your app's symbols." This just worked for me after I found the workaround on twitter. Maybe this way I can at least get the iOS14 fixes out before the weekend.