I've asked about this before, but wondered whether anyone had found a solution yet.
On calendars I like the week to start on Sunday. I have a paper monthly calendar which has the same info I have on Lightning -- with the week starting on Sunday. But every few weeks Lightning changes to the week starting on Monday. I have to go to Settings, reset it to Sunday (there's an option to start the week on any day you like), close Tb, relaunch Tb and check Lightning, and it's starting on Sunday again. For a couple of weeks. Then it reverts to Monday.
Other settings remain as I set them, even when there's a new version of Tb (except a few weeks ago, inexplicably, it completely messed up the columns I have showing in my Inbox etc) -- so why won't this setting stay as I set it? Is there no way of forcing it to stay put?