Further update, I’ve given up trying to get my large files to sync when copied in all at once, copying them into the synced folder one at a time is working and getting them onto OneDrive. Having spent literally an entire day trying persuade the last batch of files to sync when all were copied in at once, removing them from the folder and copying them back in one at a time is givng upload speeds that will probably allow me to complete the task in about an hour. So the ability to limit the number of simultaneous uploads is critical if you work with large files.
Also, looking around the forums I see that this was promised as a feature for v2 of Insync in 2016. Where did it go.
Furthermore, I have found that if I pause the large uploads for an hour or two because I need the bandwidth for work, they frequently re-start from 0. Again, if less were uploading at once, this would be far less of an issue.
Sorry for the rant, but feeling a bit short-changed at the moment having recently purchased InSync only to have it fall over this badly the first time I try to use it anger, when a seemingly simple feature that ought to have been there from the start would solve the problem.