I noticed this issue after upgrading to fabric-1.18 - 3.0.20. When using animation builder like so:
AnimationBuilder() .addAnimation("attack", false) .addAnimation("idle", true)
The attack animation would play normally, but the idle animation does not loop afterward. I have a temporary fix currently that replaces the loop with .addRepeatingAnimation("idle", 20) but I was wondering if something changed. Setting the idle animation without any other animation before it like this also works as expected:
AnimationBuilder().addAnimation("idle", true)

Will be fixed here soon