See https://discourse.phabricator-community.org/t/unable-to-quick-select-copy-task-number-and-custom-fields/3262/ and https://discourse.phabricator-community.org/t/copying-and-pasting-the-differential-number-pulls-in-differential/3251/.
Both threads report bad double-click selection behavior in Chrome. Since the behavior is fine in Safari and Firefox, the underlying markup has explicit spaces aimed at effecting the desired behavior, it seems likely that this is a change in Chrome.
I'm going to try to find an even simpler and more-obviously-broken test case since our I think our markup is extremely unambiguous.
I originally noted this similar issue, but no longer believe it is related:
This comment in the Chromium bug tracker suggests it may have changed in Version 77:
That bug has a simple test case which now fails, so this is very likely a regression.