ZDoom

Last GZDoom (g3.6.0). Please, look my video again from the first post here. I demonsrated sound breaking after first playing of sequence. Activate trigger first time and wait end of the sequence.
The video also indicates an obvious bug with SNDSEQ when using the Platform (timecode — 1:02). overlaying the start sound with the middle is broken. In the example for you, try to test the elevators. The first two on the left exactly have incorrect sequence playing.

I'm sorry but I cannot hear anything wrong when I try to open those doors. What versoion of GZDoom are you using?

I deleted access to the file, thanks for you let me know. And may you test Door with DoorHell2 Sequence? I really can't understand why it's not working. This seq don't wanna play open sound :c

I just downloaded it, in case you want to delete it quickly.

Here you go: https://drive.google.com/open?id=1bAUxtFbmY_G7vnVcl9epxqdlwbwwcRX0
Put in the console "map test01" to launch testing map. After this, open two first doors left and right of you. First action executing with SNDSEQ breaks sounds before "stopsound" line. But when you will try open door again it becomes OK.
In the end of room open hellish door and test elevators. Some of them has broken sounds, which hasn't crossfade with "middle" loop sound.
p.s.: this archive is private, I am waiting for your reply.
p.p.s: and plz sorry for my terrible English, I didn't use the translators while typing this reply, because I am really have no time now.

We cannot debug a video. I have absolutely no idea what you are trying to tell.

Plus elevator start sound hasn't crossfade with "middle" loop sound
detailed demo and proofs: https://youtu.be/the4xpeYk7U