Since the patch is not live yet i can say that this report follows the rules and i can post it here.
I'll talk about everything that was changed on Illaoi since 9.9 regarding roots and groundings
Casting W + attack worked both melee and dash range.
Attack + cast W worked both melee and dash range.
Casting W + attack only worked for melee.
Attack + cast W worked for both melee and dash range.
Casting W before being rooted + attack, only works for melee.
Attack + cast W, doesn't work. Casting W is disabled.
Casting W+ attack, only works for melee.
Attack + cast W only does melee W, but uses the dash range.
So casting W + attack works fine since 9.11.
The issue here is what happens if Illaoi attacks and then casts W, which is what has been tried to be fixed since 9.11.
Before 9.18 she dashed. On PBE currently she doesn't dash, but she's still allowed to melee W at dash range.
This is the last step to completely fix illaoi using dash w while rooted. If she attacks + casts W she should only use W if the target is in melee range. She's not supposed to melee w at dash range.