Well I think this problem may have been solved, using a very old solution (pun intended).
Back in the day, washer bottles were filled up with water and a bit of washing up liquid. At some point, decades ago, after washing cars for years with washing up liquid, some bright spark pointed out that it contains salt and should not be used.
On a whim, after finding that my purpose made screen wash was actually pretty sh1t at cleaning the windows I decided to try adding a small drop off washing up liquid to reduce smearing.
It worked a treat!
Decided to put some into the GF's Jazz as we both use the same screen wash...
After one tank of screen wash and washing up liquid the washer jets are working as per Honda design
Coincidence?
I suspect not!