Strange Non-Crank issue

Hello, i hoping someone can help with this. (I'm a Audi master tech, but Subaru do work very differently as I've learnt over the years of owning this car)

So recently my car has been having a non cranking issue, I'll turn the key but the engine will not turn over. sometimes i can get it to work if i turn the key a million times.

I am getting 12v to the starter motor switch and can hear the starter make a click. beck of the findings i decided to replace the starter motor, and i also did a new battery at the same time. unfortunately I'm still getting exactly the same issue.

when the fault is happening if i short the starter motor out it will start the car no problem. this has made me think there's an issue with the relay, now I've not been able to find anywhere that tells me the exact relay. i have pulled all the relays out from under the drivers dash and have still got voltage going the the starter, so not sure what to do with the relay.

I have also been getting a stalling fault at the same time, when i push the clutch the car will stall. i found that the clutch switch is on the same system as the starter system. I replaced the clutch switch with a new one from Subaru, and this has help a lot, am no longer getting the stalling issue and the starting issue has been reduced.

back to the starting issue.

so when i fitted the clutch switch the car still wouldn't start unless i used the power probe in the starter, but as soon as i put the battery charger on it started 1st time. i have checked the battery which is testing perfect, and the alternator is charging as expected. I have been able to reduce the fault from happening but fitting my motorbike solar panel trickle charger but does pop up now and again so the underlying issue is still there.

I am running out of ideas of what to check next and would greatly appreciate any advice and help. Plus would really like to know what relay and where they are in the car (believe there are 2, B422 and B225 but not sure)

Thanks for any help. (my car is a 2006 Subaru WRX STI PPP)