Here is the config and test data!
# dec/19/2019 09:26:31 by RouterOS 6.44.6
# software id = NLIW-GDHR
#
# model = RBwAPR-2nD
/interface lte apn
set [ find default=yes ] add-default-route=yes apn=internet default-route-distance=2 name=default use-peer-dns=yes
/interface lte
set [ find ] apn-profiles=default disabled=no mac-address=AC:FF:FF:00:00:00 mtu=1500 name=lte1 network-mode=gsm,3g,lte
# DEVICE VENDOR NAME SPEED
0 1-0 Linux 3.3.5 ehci_hcd RB400 EHCI 480
1 1-1 MikroTik R11e-LTE 480
interface lte cell-monitor lte1
PHY-CELLID BAND EARFCN RSRP RSRQ RSSI
103 B1 500 -106dBm -19.5dB
182 B1 500 -110dBm -16dB
458 B1 500 -111dBm -19.5dB
interface lte scan lte1
Flags: C - current, A - available, F - forbidden
OPERATOR MCC-MNC ACCESS-TECHNOLOGY RSSI RSRP RSRQ
C A1 21910 Evolved 3G (LTE) -96dBm -11.5dB
I just entered interface lte set lte1 network-mode=3g band="", but that earlier didn't work, so we had to turn on LTE back again.
UPDATE - it didn't work again. We had to turn LTE back on again.