The bug
The nether portal broke, but its sound still playing.
How to reproduce
Build a nether portal
Wait until it plays sound
Break the portal, but sound didn't stop playing
Linked issues
relates to
Attachments
Comments

Might relate to MC-94956, perhaps that issue can be looked into again since individual sound events can be stopped using /stopsound.
Confirmed for 1.13.1.
This is easy to explain why its happening;
The nether portal sound is around four seconds long, if you break the portal while the file has played only one second, it will continue playing the file untill its stops.
You can test this yourself by doing the following:
Make a portal.
Execute this command: /playsound minecraft:block.portal.ambient player @p
Break the portal.
If the timeing is good you'll hear the sounds stop at the same moment.
Can confirm in 20w48a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 1.17.1.
still in 1.19.4 and 23w13a
In 24w05b
In 24w37a and related to MC-210411
Can confirm. Sounds don't stop instantly when the nether portal is destroyed.