Wither Still Floats Above It's Target When It Is Below Half Health Despite Being Immune To Arrows Still

During the wither fight, the wither is supposed to descend to the level of its target at half health or less (when it gains arrow immunity).  When I fought the wither the first time on 21w42a in my original world, I got it down to below half health and it was not coming down to my level.  However it still gained immunity to arrows making it impossible to kill with a bow or sword when it was below half health.  It regened enough health to regain its floating ability and it then I proceeded to reduce its health to below half for a second time and yet again, it still did not descend to my level making it impossible to hit with a sword while still being immune to arrows. (I attached a video where I retested it on a different world also on 21w42a and the same thing still happened).