Probably already done this, but I’d make sure the APN is right - those log look like it’s not getting an IP address, which could mean some specifical APN setup may be required.
If you’re in Europe, another option be hAPaxLite6-LTE: https://mikrotik.com/product/hap_ax_lite_lte6#fndtn-specifications . Not the fast modem modem on market, but good value and seemingly good reports. That also give you a backup router as well and/or perhaps management Wi-Fi network for the routers. Since connect to RB5009 via ethernet, so you can get something like a hAPLite in perhaps better location for signal than a USB stick modem in the RB5009 USB port too.