some more details just found:
when setting static route on client the rdp connection is stable, no problems or timeouts.
(I guess client does not go through srx to reach remote subnet)
back to the issue:
Im not sure the return traffic passes the srx which may create assymetric flow?
is there a way to allow this or somehow to prevent the srx from blocking the communication or maybe somehow make all traffic pass the srx to create symmetric flow?
thanks