Highly granular custom map only patchily coloured in

Hi I have a model that looks at population statistics for England at what is known as MSOA level which is a fairly small geographic unit used by National Statisitcs. MSOAs can then be grouped into Local authorities and upwards.

the modle is here https://www.dropbox.com/scl/fi/n9s04lm5n0csuqqxtz4qb/Trial-Provider-2011-Basis-Updated-May25-V2-Depression.pbix?rlkey=r10e3g2jyfwspnmiuqu5movem&dl=0

On the first tab I used a cusotm map for LA I got frm Nat Statsiics and works fine with every LA coloured.  On the last tab I tried ot use a new cusotm map at MSOA level which you can see is partically working.  Inthe right hand table you shoudl get the results of clickingon an area in the map. For example if you filter the rights hand table for MSOA = Mid Sussex 004 and Mid Sussex 006 you get 2 results both with a population.  On the map only 004 shows in red, but of you filter the table and click on 006 it also shows in red on ther map. So this rules out some slight spelling differences or spaces in MSOA names.

So it seems the calcuations are fine, but there is a rendering issue. I tried publishing online, but looks the same.  Is this just a limitation of mpas that this is too high a granularity for it to cope with?  Any way round it? Any alternative mapping tools that will take a json file?

Thanks for any advice

Mike