Can we assume that you are using the latest version of Shotcut (21.03.21)?
Some problems in Shotcut occur when the computer does not meet the minimum requirements.
Here I link additional information to rule out factors.
Shotcut - Frequently Asked Questions
In case you do not know how to incorporate additional information, we will guide you on how to proceed and advance on what is happening.
Sometimes a screenshot of the project gives us clues about certain things.
Here is a recent example of a user with export problems. You can see how he provides information and how the issue evolves to a conclusion. This is not like your problem, just an example.