I solved the problem yesterday in a drastic way. I simply clean installed MacOS Mojave, by wiping out my ssd before. Then I used a time machine backup to transfer back all my data and apps. Everything runs smoothly know.
However, it seems that there was a specific kernel extension which was causing the problems on my Mac. It probably interfered with other apps on my machine apart from PhotoLab2 and Filmpack 5. With the clean install I managed to isolate and hopefully eliminate this issue. The kernel extension was Joshua Wise System Software driver.