Common problem with all anodised rims, I've had it happen with DID. Morad and Takasago rims , the anodising gets compromised usually at the valve or spoke holes or where the anodising is scratched due to tyre irons , combine it with people using washing up liquid to get tyres on (full of salt) and corrosion gets established , the alloy under the anodising corrodes and the rim starts to delaminate.
in extreme cases ie gold Honda trail bike rims the outside of the rim can look okay until you remove the tyre and find that the rim consists of an outer layer of gold anodising a rim about 1/4 of the thickness it should be and a load of grey aluminium powder . I had a Transalp rim that once the rim was de - spoked I could physically bend the rim in and snap it into 2 pieces .
Best be is remove the tyre and if the corrosion isn't too deep clean the bead area and inner well with a rotary wire brush removing all corrosion and loose material and then spray it with a good quality acid etch paint , get the tyre refitted using the black rubberised sealing compound that all the car tyre fitters use on corroded car alloys and that should cure the problem.
This is a Morad rim that on the surface looks fine
