While playing Arena, I enchanted my opponent's Slimefoot, Thallid Transparent, which was their Ring-bearer, with Witness Protection. I expected that Witness Protection's ability removal would remove the one ability that The Ring's had at the time, "Your Ring-bearer is legendary and can't be blocked by creatures with greater power". It's a simple matter of timestamps, right? First The Ring gives Slimefoot the ability, then Witness Protection removes it. However, it did not. Here is a screenshot:
Thinking this was simply a visual bug, displaying the ability without granting it, I attacked with Dina, Soul Steeper and passed. On my opponent's turn, they attacked with Legitimate Businessperson, and I was not given the option to block it because all my untapped creatures had 3 power. This confirms that the ability was functional.
9 times out of 10 I can mull it over and prove myself wrong when I think there's a bug in Arena, but I'm stumped here.