I have made a new version of my diagnostic tool for Time Machine backup problems, The Time Machine Mechanic (T2M2), which has been ported to Swift 3.2 and built using Xcode 9. This should now be fully compatible with both Sierra and High Sierra.
I have not yet had a chance to analyse the log messages in High Sierra which T2M2 relies on, so this version should be considered to be of release quality for Sierra, but of only beta quality on High Sierra.
I have also made a minor fix, which displays floating point values better. Instead of them appearing as ‘5.0’, they should now be shown accurate to that first decimal place, such as ‘5.2’.
This new version is available here: t2m211b
and in Downloads above.
Please let me know how it gets on in High Sierra.