sshd on yocto linux consistenaly disconnects me

We have our own yocto image on IMX8 device (NXP). The device internet is served by simcon EU 4G modem and IOT sim (Monogoto). The connection id created with libqmi and created wwan0 successfully. - the sshd recipe was left untouched (expcet for preventing root logins) - the ssh access to the device is on demand, when requested ngrok forwards TCP port 22 and on ngrok site i can see my URI to connect to. When trying to connect i'm successfull. However when i try to use commands with large output like dmesg or copy paste large test files to vi the terminal hangs and connection shuts down. If i connect using ngrok to a regular PC the connections remains open just fine. I thought it might be the modem. So i connected to my ubuntu using a USB similar modem (EC25e - same SIM provder though) the ssh connection was ok. Tried to compare and change the sshd_config settings but all the settings that were different between my laptop version and the Compulab (NXP) and were changed did not seem to help. Any idea as for why the disconnection ? Any lead ? Thanks.