Heater matrix core

Ive had a problem with heater core matrix since last year. Ive diagnosed the issue using vcds ive checked flap motors, all the data and had a 20° difference from left to right, then i proceed to chsnge the matrix core then it worked perfect for 3 months then again. So i started with flushing whole circut with water then added destilled water a then radiator flush. After all that ive installed new nrf heater matrix core. Last night it happened again passenger side warm and driver side hot as hell. What to fo wity it now? Changed it for the third time? Flush it? Dont know what to do and Im tired of it already. Someone hade similar issue?

( no silikat in the bank, changed couple of time to g12evo, no problems with flap motors, as skoda says my car went through procedure of flushing in 2020)