Where did you get a Swift 5.5 toolchain for arm? AFAIK, nobody provides such a build, did you build it yourself? Or are you using the new official trunk snapshot builds for ARM? That branch is more early work towards the next Swift 5.6 release.
Can you reproduce with the unofficial stable 5.4.1 builds for AArch64? If not, this may be a regression in whatever unstable branch you're using.