Hello. Hope you are all doing well. God knows I am not. 
I used to have a super annoying problem with my LHG-LTE18 constantly lagging, crashing, and misbehaving in general. I am not going to go into great detail here, but for anyone care reading (although it does not matter any more, at least to me) you can find the old post here.
Long Story Short, I never got to fix the problem I had. Tried updates, downgrades, fresh netinstalls, different configs, almost anything I could think of. Nothing worked.
Then, I went ahead and asked you guys, (here) if I should just go ahead and buy a new device since mine was very clearly malfunctioning and it was almost definitely not a matter of wrong config, and if at the same time, instead of getting the same one, I should upgrade to the ATL5G R18.
Got mixed feelings and suggestions...
...but I went ahead and bought the newer, 5G device.
Installed it. HO-LY-CRAP. Speeds went up to 850Mbps. Pings really low. My internet was on fire. I can't even begin to describe how happy I was. "To hell with the 350 euros. Who cares, at least this works". I thought to myself.
Little did I know that my old nemesis was back.
A few weeks after I first installed the device, I randomly lost connectivity. Okay I though, sometimes this happens.
Then a couple of days, again. Then again.
A couple of days ago, the device might have crashed like 30 times. It drove me insane.
What's happening, and I want to be clear about this:
THE MODEM seems to be the issue. Or at least where the issue is happening.
I ALWAYS have connectivity to the device, it never lags, I can run all comamnds, the UI in winbox is responsive, and I do not see anything close to what my OLD device did. This issue is completely NEW.
(The old device wasn't losing connectivity, it was rather becoming terribly slow and unresponsive).
I did consider overheating, since this summer is hot, and especially in Greece, although the device is designed to be used outdoors in direct sunlight, but overheating is not the issue I think, since the problems sometimes happen during the night as well. The night is pretty cool here. If it was an overheating issue, it should happen only, or MOSTLY during noon, when the temp is at its peak and the sun is the brightest.
Does anyone have any ideas ?
Because I am literally 1 click away from going back to a chinese router. I am beyond frustrated. 
My RouterOS and modem Firmware:
version: 7.20.7 (long-term)
RG520FEUEAR03A04M4GX_01.300.01.300
My config:
[bonamin@ATL5G-R16 Modem] > /export
# 2026-06-28 10:00:10 by RouterOS 7.20.7
# software id = 2DP7-TG9V
#
# model = ATLGM
# serial number = HM80B6D98GW
/interface lte
set [ find default-name=lte1 ] allow-roaming=no band="" network-mode=lte,5g nr-band=""
/interface vlan
add interface=ether1 name=management vlan-id=2
add interface=ether1 name=network vlan-id=3
/interface list
add name=LAN
add name=WAN
/interface lte apn
set [ find default=yes ] add-default-route=no name=cosmote passthrough-interface=network \
passthrough-mac=auto use-network-apn=no use-peer-dns=no
/port
set 0 name=serial0
/interface list member
add interface=management list=LAN
add interface=lte1 list=WAN
add interface=lo list=LAN
/ip dhcp-client
add interface=management
/system clock
set time-zone-name=Europe/Athens
/system identity
set name="ATL5G-R16 Modem"
/tool sms
set port=lte1 receive-enabled=yes
and you can find a few logs from the past couple of days here !
This is my reality now:
is this a known issue ?
Should I upgrade anything ? Damn I am confused.
Anyway, thanks a lot in advance.