Shotting an arrow or typed arrow with a crossbow enchanted with multishot does not apply the correct damage per arrow and only calculates the full damage from one arrow.
How to replicate this issue:
Get yourself a crossbow
Enchant your crossbow with multishot enchantment
Charge the crossbow with an arrow or other typed arrow
Shot it to a very close mob
The expected result should be to deal extra damage per arrow, but here it only counts one of the three arrows. So the encantment functionallity is completely broken.
You can also check all of this process in the clip below
Please edit your report to change the Affected Version to the version shown on the Minecraft title screen