This is the reply I have got from BM:
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'Hello there,
thanks for your email
To be honest I have not seen many customers with this issue. However, I would recommend you to try to updated the GPU driver and see if it cures the issue.
Also, I would check the hard disk speed (use the utility speed test) and see whether there is a performance issue.
Regards,
Michele De Benedetti
Technical Support Consultant
Blackmagic Design EMEA'
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BM have just issued a new driver and since I have installed this I have not had the timeline issue. It is not the first time I have raised an issue with BM and been told nobody else has that problem only for the 'non existant problem' to be fixed in the next driver.