One small nit, that trunk snapshot from last weekend is no longer Swift 5.6, which branched last month, so trunk is now the basis of Swift 5.7 or 6.0 or whatever the next version will be numbered.
Do you see the same problem with the Swift 5.6 snapshots that were just released for the first time over the last couple days? Sometimes bugs go away in different branches, eg this armv7 compiler crasher I reported last month, which might help track down the cause.