The current SX126x sync word (0x0F0F) does not match with any sync word supported by SX127x. Apparently, when using 0x1424 as the sync word, the SX127x will match as long as the 4 MSb are 0x1 or the 4 LSb are 0x2 - though some combinations are more reliable than the others, for example 0x11 - 0x1F match every time.
jgromes
commented
4 years ago
The current SX126x sync word (0x0F0F) does not match with any sync word supported by SX127x. Apparently, when using 0x1424 as the sync word, the SX127x will match as long as the 4 MSb are 0x1 or the 4 LSb are 0x2 - though some combinations are more reliable than the others, for example 0x11 - 0x1F match every time.