I think this is the same issue I raised here: Issue with routing and multi-page SPA site (hybrid MPA)
Unfortunately, I received no replies to this so thought it must have been a silly question and the answer too obvious to mention (but not to me). I was only experimenting withi SPAs at the time so didn’t pursue it.
After that I decided not to use SPAs for the time being, but I’ll be interested to see how this thread goes. (Of course I may have misunderstood and perhaps the issue is not the same.)