Caravan brakes locking up at cruising speed

Is it possible it sensed a bit of sway and did what it is designed to do?

jb
It could be a number of things. "IF" your vehicle brake controller is loose on it's mounting OR not secured to a stable surface it may be flapping whenit experiences a sudden bump and subsequently applies the van brakes fully ON for a short period of time. Since there is a residual magnetic effect in the brake magnets they may hang on for a second or two.
Secondly, if wiring in the trailer plug is not good inside, some intermittent conection with park light system may be applying the brakes when flicked. Check the wiring in there.
Thirdly. Breakaway system wiring may also be doing similar if wiring isn't secure.
If electricals are proper, the adjustment of brake shoe clearance may be an issue. When sudden bumps may throw large clearance shoes against the drum and the subsequent "servo action" of the brake design will jam the brakes fully ON until the shoes can settle themselves to a neutral running position.
Have you had some sudden grabs of van brakes during normal use? If so adjustment could be a problem.

Thank you for those suggestions - will check them out.

Cruisemaster trailer brake lever has a problem there is a recall maybe worth a look cheers

To check if it is the AL-KO controller, disconnect the power from it and see if the problem keeps reoccurring.

Thanks. How do I disconnect it?

Thanks for all that helpful information - I will contact the caravan maker & follow up your suggestions. Most appreciated !