Anyone else had grief with a Victron MultiPlus 12/3000 cutting out under load? Need some advice

I've had my MultiPlus 12/3000/120 for about 18 months now, running it off a 400Ah lithium bank (4x 100Ah Epoch cells in parallel). Up until recently it's been rock solid, but over the last few weeks it's started tripping out when I fire up anything with a decent startup surge — the main culprit seems to be my 1200W kettle, which it used to handle no bother at all.

When it trips, the unit flashes the amber overload LED three times, then shuts itself off. It usually comes back on fine after 30 seconds or so. I've checked all the cable connections and nothing looks loose. The cables are 70mm² from the battery to the inverter, about 800mm run, so I don't think it's a voltage drop issue — though I suppose I should actually measure it under load rather than just assuming.

I'm wondering if it could be a temperature thing — the unit is mounted in a fairly tight wooden enclosure inside the van and we've had a warm spell lately. I've not fitted any additional ventilation in there. Could the thermal management be getting more aggressive as the unit ages, or has something actually degraded inside? Has anyone had similar with a MultiPlus and managed to trace the cause?

@Barry1965 — worth checking your battery cable lengths and gauges before anything else. I had something similar on my narrowboat last spring; turned out one of my parallel cables was fractionally longer than the others, causing uneven current draw across the cells. Under heavy load the Victron was seeing a voltage sag that tripped the low-voltage cutoff, even though the bank as a whole was fine.

Grab a clamp meter and watch the current distribution across each cell during a big load spike. Also check your busbar connections — mine had developed a tiny bit of corrosion that wasn't visible to the naked eye but was adding enough resistance to cause grief.

What's your cable spec between the bank and the MultiPlus?

Good shout from @HalfAJob on the cables. One thing I'd add — have you checked the temperature compensation settings and whether the BMS on your Epoch cells is actually communicating properly with the MultiPlus?

After 18 months, it's worth looking at whether the MultiPlus is receiving accurate state-of-charge data. If the BMS is throwing a protection cutoff rather than the inverter itself faulting, you'll get identical symptoms but a completely different fix.

Also, what's the ambient temperature like where the unit's installed? I had mine cutting out intermittently last summer and it turned out to be thermal shutdown — the ventilation gap I'd left wasn't sufficient once the weather warmed up. Added a small 12v fan nearby and it sorted itself completely.

What does the LED pattern look like when it cuts? That'll narrow things down considerably.