If you have a sync problem in Shotcut preview, then I think “import” is somewhat accurate although technically it is merely opened instead of imported. If that is the case, then you can to try to convert it using Properties > menu > Convert to Edit-friendly… You need to open the new file; it does not open automatically. You can double-click the completed conversion job to open it.
Thanks for your reply. Bizarrely today when I go to try your suggestion I opened up the video and it was all synced perfectly. Maybe my machine is struggling to cope with the job. ???