ECU - Interface closed

Need some help please.

I have a Subaru 2005 Forster XT, bit of a project car. I had a WRX 2012 gearbox (manual) and diff in the car. Car was tuned twice with no issues. I manage to source original gearbox to get speedo working again. Since the speedo is working again the car revs hangs. When I drive and you change gears I noticed that revs does not come down immediately. Just stays there for few seconds. When car comes to complete standstill with clutch engaged and still in gear the car will rev up to 2000rpm and stay there for few seconds before returning to normal. I noticed that when I put that car in neutral the revs will come down immediately. When I unplug the speedo the car operates as per normal before gearbox swap.

So back to tuner I go. Only problem now is that two different tuners with different hardware and software cannot get the ECU to flash anymore. Both tuners can read the ECU, but when they want to flash it, it just says "Error" & "interface closed". I even had another ODBII port splice in and same issue.

Any suggestions? Thanks