I don't have any backups currently, iCloud was full. It's not a big deal, at least I understand a few more of the many quirks of iOS now.
It did the thing of showing the launch screen for a second then vanishing... so didn't even launch.
I'm having a few more issues though, I've been setting up my midi control settings though, and testing them out I'm finding few quirks:
1/ The dialogue to allow GTL to set the tempo seems to be gone, and I can't find the option in the clock settings were I think it used to be.
2/ I can't seem to set the number of bars for my initial loop. the clock multiplier buttons were showing divide and multiply, but I wanted minus and plus. When I changed them to that in the clock settings, they greyed out and were inoperable. I changed them back, but they were still greyed out.
So the upshot of that is I can't seem to get GTL to set the tempo based on my first loop, with a pre-selected number of bars. I seemed to be able to do this reliably before, and I'm not sure whether I've forgotten some crucial thing (I don't think so) or whether something has broken.
And I'll @[deleted] this for good measure!