There is one test case in editing/selection/user-select-all-with-shift-live-range.html that starts failing when enabling live range selection. It's actually a pre-existing bug but live range selection makes it more prominent.
Pull request: https://github.com/WebKit/WebKit/pull/6725
Committed 256964@main (2d2117dc6166): <https://commits.webkit.org/256964@main> Reviewed commits have been landed. Closing PR #6725 and removing active labels.
<rdar://problem/102618102>