I am sorry that you are having issue with SXT LTE in Spain,
This is our first lte product, We have certified it and it should work in both 3 and 7 lte band in all available Channel
bandwidths (1.4, 3, 5, 10, 15, 20 Mhz ) We tested it in different markets before launching and we did not encounter issue with connecting.
/interface lte scan lte1 is not supported command for SXT LTE, It will connect automatically to network based on sim information.
Other thing is that in some countries operators have white list of vendors imei that they allow on their network. Have you tried different usb modem that is not from your s country's operators ?
Also please send more supout.rif file with latest 6.36rc to
support@mikrotik.com with added.
/system logging add topics=lte