after updating Shotcut from 19.06.15 to 21.01.29 every mlt file created with the older version causes an error message:
“Shotcut noticed some problems in your project. Do you want Shotcut to try to repair it?”
Regardless of what I choose (“No” or “Yes”), the project file is opened and seems ok. Why this message?
You may find it benificial to keep a copy of 19.06.15 available(the portable zip version would be fine) for projects like this since as @Somenath_Garai mentioned certain filters have been deperciated. old releases are still available on github.