If I encountered that situation (progress bar hits a stop point) I'd try the corrupted file route.
I'd first 'Save As' and see if the new file exhibeted same behavior.
If so, I'd start looking at the file and try to find some 'glitch' .. I'd start by checking audio events triggered later in the song. How much later may be related to how far the progress bar got.

If still stuck
Before giving up, try File - Open Backup
RB does make a backup of the previous version saved. See if that renders OK.

I assume other seq files render OK (?)

I do not work here, but the benefits are still awesome
Make your sound your own!