sounds exactly like my scenario over here: Electron G350 connectivity (flash sequence)
I just get the feeling (in my scenario) its a composite problem of SIM connection (holder), carrier signal, and data provision. MVNO’s often get a worse deal if the tower is busy and at certain times of day - this makes testing a problematic issue for me, although my 2g phone is able to send TXT its so old it cannot do data :(. My proper phone is 3/4G so its not a good comparison for Electron G350.