Steps to reproduce

1. Equip armor enchanted with thorns.
2. Walk through a sweet berry bush, across magma, or into cactus.

Expected results

You get hit and take damage every 1/2 second. Armor durability goes down normally.

Observed results

You get hit rapidly while not necessarily taking damage, and armor durability goes down rapidly.
Rapid hits.mp4

When wearing Thorns enchanted armor, for some reason, the game appears to skip the "invincibility frames" when taking damage from magma blocks or sweet berry bushes. It also appears to use more durability on all of my armor.
Note: I am playing in Bedrock Edition 1.20 Beta. Device is a Samsung phone (SAMSUNG SM-A125U according to the debug text on-screen). I have Max FPS set to 30, simulation distance set to 8 chunks, and render distance at the minimum. Not sure if the last three would help in any way but I thought I'd include them just in case.
Also, I am playing on Bedrock Edition, not Pocket Edition.
EDIT: While doing further testing, I noticed that having the Resistance effect can "cancel out" the bug, even when wearing Thorns enchanted armor.