Cellular connection dropping whenever a journey started.

I have an OVMS installed in my 2020 Nissan e-NV200 which has generally worked flawlessly for a couple of years, but for at least the last year or so I have been experiencing a recurring issue where the cellular connection drops shortly after starting a journey, from any location

The behaviour is very repeatable:

if I reboot the OVMS and leave the van parked, it can stay connected for days without issue, but once I start driving, the telemetry connection will often fail within a short time of setting off.

The OVMS itself remains alive, but the PPP/cellular connection drops and telemetry stops working until I reboot it again.

I am using:

SIM7600 modem

Hologram SIM

usually roaming on O2 UK

Some diagnostics I have run:

modem still appears registered on the network (+CGREG: 1,5)

CGATT remains attached

signal strength is generally good

PPP shows “Not connected”

CEER returns “Requested service option not subscribed”

This is making me wonder whether the issue may relate to:

LTE roaming handoff

Hologram/O2 interoperability

PPP reconnect handling

or possibly power dips affecting the modem during movement

Has anybody else seen similar behaviour, particularly with:

SIM7600

Hologram SIMs

UK roaming networks

or OVMS in Nissan Leafs/e-NV200s?

If so, did you identify a cause or a reliable fix?

Hardware: OVMS WIFI BLE BT cores=2 rev=ESP32/3; MODEM SIM7600

Firmware: 3.3.005-3-g4f3f7688/ota_0/main (build idf v3.3.4-851-gfa4f07fb3b Sep 7 2025 08:02:51)

Running partition: ota_0

Boot partition: ota_0

Factory image: 3.3.001-33-g58d01654

OTA_O image: 3.3.005-3-g4f3f7688

OTA_1 image: 3.3.005-2-g40245d7b

Server Available: 3.3.005-3-g4f3f7688 (no update required)

OTA build Sun Sep 7 08:08:09 CEST 2025

Thank you.