Hi Dom,
I do NOT recommend leaving multiple USB sticks plugged into the keyboard all the time. This may be the reason for the problem described. The keyboard checks all connected storage media with every file operation, and with so many USB sticks / files it can happen that the keyboard "chokes", e.g. it takes a relatively long time for a file operation to be completed.
I generally recommend only working with a maximum of one connected USB stick. It's also easiest if you don't work with the internal User drive at all, but directly with the USB stick. You can simply back up the contents of USB sticks on the PC or copy them to other sticks and thus always have working backups. On the other hand, if you store everything in the internal User drive and then make backups of it on USB sticks, registrations in which external files (e.g. user styles) are linked will NOT work from the USB stick if the linked files are deleted in the user drive for some reason , moved or renamed. This is because the absolute file path (drive letter/folder/subfolder/filename) is always saved in registrations.
In addition, an additional main folder specified by the system is used in the internal User drive for each file type. This must also be taken into account if you want to edit registrations with linked external files copied from the User drive to a USB so that they work directly from the USB stick.
Example:
You have created a style folder "My Styles" in the User drive, in which the style "Test.sty" is located. If you link this style in a reg, the path "C:/STYLE/My Styles/Test.sty" will be saved in that reg. If you now copy the "My Styles" folder and the relevant Registration Bank file to a USB stick, the file path in the Reg file would have be changed to "I:/My Styles/Test.sty". In addition, it must then be ensured that this stick is connected first, i.e. it is recognized as "USB 1".
The second stick connected (USB 2) would be "J:/" and the third stick (USB 3) would be "K:/". Basically you can use the PC program "Yamaha Registration Manager" (YRM), developed by our forum member Murray Best, to make such path changes in reg files (also in Batch mode for many reg files at once), but for most users this "file path issue" just described is quite confusing. Therefore, as I said, I recommend managing all of your own files on the USB stick and only use ONE connected stick when working with Registrations.
Best regards,
Chris