Modbus RTU

[Omega Technology]

hi, I have a problem regarding the modbus, I have a LM with 3 rs-485 ports and on all 3 I have some timeout problems and rarely also crc errors, I manage everything via script, I have already tried to add delay between readings of the registers of the same devices and delay between readings of the devices themselves, I tried to make a log to see the error this is the most common situation , 

* string: [02][04][1A][1F][00][02][47][26]
Waiting for a confirmation...
<04><00><00><81>ERROR Operation timed out: select

so randomly I have this situation ( <04><00><00><81>ERROR Operation timed out: select ) in multiple random slave.
best regards, Omega Technology.