Hello and thanks for the reply,
I modified the 868MHz board in the following way: Replaced all the passive values to conform to the 433EM reference design, With few minor exceptions, 5.1pF capacitors: I used 5.0pF NP0, and 27nH inductors, I used multi layer (LQG series), instead of wire wound (LQW). The rest are exactly the same parts. The SAW filter was shorted.
I tested both the source carrier and target carrier, They are within 5Khz (~15ppm) of each other.
The setting above has an error, the default CC1101 has 32bit preamble and sync, and the CC1125 is set to detect 16 bits and sync. I corrected this, and the CC1125 receives packets reliably, albeit with reduced sensitivity.