Thank you everyone for your comments and advice. My bad, I shouldn't have installed this beta. Instead of doing the tedious operation mentioned by Nice Monkey I will wait for the next stable release.
@Nice Monkey: I have problem with (.sub) format. See previous posts. About subtitle (.sub) format I have not received answer. I always have to convert subtitles (.sub) to srt. And there is a problem with (.sub) format subtitle. I want you to know that it is a good device but some bugs need to be fixed.
Then you can wait till end of your life. This version was released over the official telegram account of Zidoo and works as stable as the previous betas before.
You can repeat it as often as you want but it remains wrong. It was released by Zidoo in their official telegram account. By the way new Zidoo Controller 1.6.8 was released today in this channel!
I don't have and don't want a telegram account worse on a Russian site. It may be official (or not) for Russian users as the Russian market is next to the Asian market the biggest market apparently for media players. Zidoo Controller v1.6.8 has been available on the official global Zidoo Home page https://www.zidoo.tv/Support/release_apk.html since several days. I recommend to get it there for those interested.
@Nice Monkey Why do you think it's a Russian site? The main language is English. To me it looks like the official Zidoo site from their developers.. Some of the new firmware downloads could be downloaded there very quick. No false files since more than a year. Changelogs if availabel and so on. Looks not like a Russian fan site like Olivier's from France for example. And if you wait until some file were released in this homepage you will have to wait very long. It's always the same. Zidoo is not organized in a professional way, so a telegram account would suit to their amateur behaviour.
As I asked for help on this forum concerning a loss of sound playing certain (not all) movies happening after a crash, I feel compelled to report that I solved the problem in a most trivial way. In fact I discovered that presumably during the crash the setting Settings/Sound/Media volume was nullified. Setting it back to a 50-70% value everything is back to normal. No need for ROM-flashing and reinstalling the firmware. Now, what is most interesting is that the aforementioned setting does not affect the output of all sound formats (decoders). Interpreting this result requests a deeper than mine knowledge of the hardware/software architecture of this box.