Sometimes there is a delay of more than 1s and sometimes it's 10s in opening the folder in android phone
Steps - More delay is there in a folder which has more than 40 pics and less delay in a folder with few pics.
Do you get the same delay in File Explorer?
(If you don't, do you still get the delay in Opus? It may be that the folder is cached by windows or the phone itself, and fast the second time anything accesses it, whether Explorer or Opus.)
In FE also delay is there for first time and there is no delay of 10s in FE while opening second time even for a folder with 332 mp3 files which is there in opus sometimes,i have tested more than 8 times to confirm.
Explorer may be caching the folder listing (which is strange since it could be out of date) but that shows the delay is coming from the OS or the phone, not Opus.
As an aside, using MTP is not recommended anyway, as it is not well implemented by Windows or Android. With Android we recommend installing an FTP server on the phone (which is very simple) and using FTP instead of MTP. This also means you can transfer everything over WiFi instead of having to plug in a cable.
to repro u have to test in opus more than 6 times and that also at various times.
If it happens in both Explorer and Opus, and only happens in Opus occasionally, then it doesn't sound like an issue in Opus. It sounds like the phone or MTP stack takes a while to enumerate larger folders sometimes, no matter which program is asking for the folder listing.
Try using FTP instead. It is usually more reliable.