When fishing without a hook, this phrase pops up and world access ends.
(Fabric 1.21.1, single play)

Connection Lost
Internal Exception: io.netty.handler.codec.EncoderException: Failed to encode packet 'clientbound/minecraft:custom_payload'(hybrid-aquatic:fishing_bobber)

Im having the exact same issue

Same issue when playing on a server. Everyone is kicked with the same error message

Will be fixed in the upcoming patch

same issue here, i found these lines in latest.log:

Caused by: java.lang.RuntimeException: Failed encoding custom payload hybrid-aquatic:fishing_bobber
Caused by: io.netty.handler.codec.EncoderException: Empty ItemStack not allowed
[26Oct2025 13:48:31.653] [Netty Server IO #1/ERROR] [net.minecraft.network.Connection/]: Exception caught in connection
io.netty.handler.codec.EncoderException: Failed to encode packet 'clientbound/minecraft:custom_payload'

hope this helps in fixing the issue

This has been fixed with 1.5.2