Oil temp light when towing

I have a vw passat 1.6 tdi 2013 (91,000 miles, I have a lot of miles to and from work daily!)

It has been used for towing for about 5 years. Maybe 6 or so trips per year, so not lots.

Last year on way home from a trip, been driving 90 mins or so and the red oil pressure light flashed on bleeped then went off immediately. 

We got it checked out and no stored error code oil was fine (gets serviced regularly) and garage thought try changing oil pressure switch in case it was faulty.Oil was changed again at that time. Couple more trips and no issues.

This year same again first trip no issues.

2nd trip , pretty much exactly same bit of road as last year same happens again. Breakdown people out, no error codes, oil fine can't gind any issues. Driving back and forth to work dally (approximately 40mins each way ) no issues.

Next trip got to destination,  no issues 

Way home exactly same bit of road! oil pressure light flashes , bleeps and off immediately. Then flashes intermittently but no bleeping. Pulls over engine off , oil level fine, back on doesn't happen again.

Back at garage,  they have no idea ! Nor does my mechanic brother in law so I thought I would ask the wider caravanning community if anyone has any thoughts etc?

I should also say no power loss, rattles, noises smoke etc

Many thanks