When I find a resolution to an issue that there is very little help for or no record of on any other sites I like to throw out a quick and dirty blog article to help someone in the future. This is one of those.
Having installed the Apple Wi-Fi for iOS debugging profile I got the following error every time I tried to save some logs on my iPhone 12 Mini running iOS 14 .7.1
Failed to save logs
The Wi-Fi diagnostic logs were unable to be saved correctly.
I resolved this issue by performing a start of the iPhone (press Vol Up, then Vol Down, then hold the Sleep button until you see the Apple logo.
It was that easy.
Remember that this profile creates huge logs (Gigabytes!) so if that doesn’t solve your issue make sure you have enough space on the device and limit your testing if possible to under 60 seconds.