For a long time, I have been using XV as the smplayer output video driver. My system is Ubuntu Mate 18.04 64 bit.
I updated MPV to the latest version in July 2020 and after that whenever I took screenshots the screen froze and smplayer crashed. This happened on all occasions when I took a screenshot, but otherwise XV worked fine. The same problem occurred regardless of the hardware acceleration settings. I even re-installed the smplayer with the 'factory profile settings', but with the XV. driver It was still the same problem. Because the screen freezes and smplayer crashes, I do not think that I can produce a log.
When I changed the smplayer output video driver to Default or GPU the screenshot function worked again. So, the path to the folder is correct.
In the end, I re-installed an older version of MPV and the the screenshot function with XV works fine.
I am happy using the older version of MPV temporarily and I am only mentioning this problem now in case the same problem occurs in the future with other users.
If the smplayer can nolonger support all the functions with XV in future, please let me know at your convenience.