Deleted
It’s now 5+ months since I reported this fault, despite having a long web chat with BT, still not fixed. Very disappointing.
The app was updated in October to version 8.34.1, have you tried that.
Also have you tried deleting app cache and data from your phone and starting from afresh.
The process may vary a little depending on your phone but generically it's something like Settings/Apps & Data/MyBT
Thanks for the suggestion, have tried as you suggested, but app still shuts down as soon as it excepts my pin, happens on both iPhone 13 and iPad Pro. I’m quite techy but have come to the conclusion it’s just not going to work for my equipment and will just have to use the web interface instead.