MP4 video don’t playback anymore after upgrade to 17.0

Hi all, i’, asking for help because i don’t know anymore how to debug this.
i’ve a PC x86 platform with the installation of the old 15 kodi ISO version, so linux based, ubuntu, kodi and Lubuntu desktop, Nvidia graphic with 303 driver installed.
i’ve keep the system upgraded few time a year, so yesterdey i’ve made the upgrade from 16 to 17.0 krypton, using packet manager from lubuntu, searching all new package and installing it.
i found that all it works good, i’ve ripristined confluence skin to have it working same as before, the system asked me to identify again the direcory for film and tv series and redo the scan, i’ve played a few pieces from films and similar in AVI, all working well…
until i’ve tried to play an MP4 video.
when i’ve tried it, what i’ve seen is a flickering image in primary color, and after it a black screen, but i continue seeing the voices and sound of the video.
trying to giv a “0” command to see what codec are doing give me no data, because the only thing that i can see is a “00:00” output, that i can’t interpret (maybe the video still remain on the first frame?)
consider that from the selection interface i can see the picture grabbed from the video as a thumbnail.
i’ve tried to see if it can be a graphic driver problem, so from lubuntu i’ve installed VLC that show me the MP4 videos perfectly.
it cannot be a permissione problem because the same files was perfectly read from version 16.
it keep the same behaviour independently from what point in the interface i use to come in (video, tv shows, film)
the only other strange thing (but is an old problem that i have still from 16 version) is that when i reboot the PC, the image presented of kodi interface is 1/4th of the screen (i’ve an optoma video projector connected on HDMI1) and ‘ve to go to settings – video – output and switching ftom default to HDMI1 (or vice versa) to have the correct full screen image.
i’m quite desperate because the majority of our videos are in MP4…
can someone give me some hint to investigate?
some solution that i’vent found?
it’s impossible that the problem is in the kodi codec for mp4, it’s integrated in kodi himself, so some million users haven’t to see mp4 anymore….
please, help 🙁