Hookless rims are designed to seal by being tight against the shelf of the rim, not the sidewall of the rim. Its also what holds them on with there being no hook. (pic for descriptions)
Are you saying the tyre is pulled off the shelf and into the centre well/recess of the rim? Youd only really expect that through excessive cornering at low pressure (i.e. Cyclocross or mtbing).
It might be that the tolerance of the tyre and rim is not a good match, with MTB tyres this used to happen as tyres aged, not sure if this happens with road tubeless as their bead tends to be stronger to handle higher pressures.
You could look to either take up some of the tolerance with an extra wrap of tubeless rim tape, or go belt-and-braces by creating a sealing hump on the rim shelf using a thin strip of tape in the middle and a full width piece over the top.
Many (MTB) tubeless rims use a flat shelf as its easier to fit (and remove) a tyre, and is usually safe.
Most road tubeless have a 'hump' on the side edge of the shelf to help hold the tyre bead against the flank/side