Is that MLT created with the same version of Shotcut you have now?
On the same computer? Same Operating system?
What type of drive is the project file on? HDD, SSD/NVME, USB, other (what other)?
Here is a sample project created with the current version 22.11.25.
Testing.mlt (1.9 KB)
I tried to duplicate your issue with this simple test project, but it worked fine for me.
If you can provide more information, like perhaps what filters and settings you are changing, I can try to duplicate the issue you are having. It would really help if you could provide a very basic/minimal project that one could easily duplicate.