Lost messages

I am working on a project with the SX1278. This is a LoRa only project and not LoRaWAN. I have a problem with the fact that I only receive 3/10 of the messages I send.
Setting modules:
Freq = 433500000
SF = 7
BW = 250 kHz
CR = 4/5

I have tried different combinations and the result is always the same only 3/10 messages. I don’t know if there could be a problem with the fact that I am currently testing the transmission in only one room, at a distance of 5 m.
I use STM32 with this library:

And a Raspberry pi with this library:

I would appreciate any advice.
Thank you

What are the RSSI and SNR readings for the messages that are received ?

My SNR and RSSI is:
RSSI: -84; SNR: 9.750000

RSSI is maybe a little low for 5M, but SNR is about right, so the signals are good.

No experience with those particualr LoRa libraries but the problem you are getting is not one I have come across with the Arduino ones.

Your not changing the syncwords are you ?

Yeah, that’ll be it. I don’t checked the default SyncWord settings in both libraries.
Thank you very much.

It seems like a solution to the specific issue has been found. Regarding LoRa networks sans LoRaWAN, this paper has proven to be very useful to my own work. They use different equipment for their nodes but their approach to building a network is most interesting. See