Rk3288 with Ec200T instabil 4g connection

We have an rk3288 based pos machine with ec200t chip, and the issue is that our 4g connection is instabil, sometimes it cannot connect to 4g just edge or 3g. Could you help me debug the issue? We have android 7 op, and ril driver.
Thank you

First, confirm whether the network signal is stable, and secondly, if the module is in ECM mode, you can switch to rndis mode to try.