I have investigated the problem some more.
DVBLink Player now seems to play the recordings without any problem. Kodi still doesn't.
I'll try to describe the problem as carefully as I can.
Raspberry Pi running Kodi is connected to WiFi network. Network connection is very good. Almost as good as WiFi can be.
When I open a recording on Kodi it starts playing almost immediately. It thinks for less than a second. It will play the recording for a couple of minutes and then stops. Message says that it is buffering. If I wait long enough it will finish buggering and start playing again, but the buffering will take 2 to 5 minutes. It will then play again for couple of minutes and buffering starts again.
If i use fast forward the playing will stop very quickly after coulple of seconds.
If I try to watch another program once the playing has stopped it won't play at all. Whole Kodi becomes then very sluggish and will only come back to normal after rebooting the Raspberry Pi.
The Windows 10 machine running the server will also have affected. It won't have internet connection anymore. Web browser will load forever but nothing will open. It does come back to normal with reboot.
I think it may be some kind of network problem on the server.
Here is a link to small recording.
https://1drv.ms/v/s!AoEaUK5GBCPQg4QfvHN2xcQgd-Pacw