I made some tries with 115200 and 38400 too... Results are the same! and using MySensors library 2.2.0, too! and using OpenHab too!
While not connected to controllers... no NACK messages, every send messages got OK... and sensors don't lose gw connection (no continuos FPAR messages)...
This is sensor log taken by Arduino IDE serial monitor (gw is connected to openhab):
Two loop runs:
in first loop one value reached gw (temperature one), 2nd and 3rd value had NACK.
in 2nd loop no value reached gw (all have NACK).
This behavior is quite usual, and it happens as soon as booted and while running for time..
Even initial presentation gets "NACK"...
Temperature: 20.20 *C
Humidity: 59.20%
Heat Index: 19.82 *C
TSF:MSG:SEND,1-1-0-0,s=1,c=1,t=0,pt=7,l=5,sg=0,ft=0,st=OK:20.20
!TSF:MSG:SEND,1-1-0-0,s=0,c=1,t=1,pt=7,l=5,sg=0,ft=0,st=NACK:59.20
!TSF:MSG:SEND,1-1-0-0,s=2,c=1,t=0,pt=7,l=5,sg=0,ft=1,st=NACK:19.82
Temperature: 20.20 *C
Humidity: 59.00%
Heat Index: 19.82 *C
!TSF:MSG:SEND,1-1-0-0,s=1,c=1,t=0,pt=7,l=5,sg=0,ft=2,st=NACK:20.20
!TSF:MSG:SEND,1-1-0-0,s=0,c=1,t=1,pt=7,l=5,sg=0,ft=3,st=NACK:59.00
!TSF:MSG:SEND,1-1-0-0,s=2,c=1,t=0,pt=7,l=5,sg=0,ft=4,st=NACK:19.82