Haven't heard about this but how would that be any different from millions of people trying to use the base chain all at once? Cuz that would obviously take a good while to process.
Discussion
It's basically the same, except imagine the difference for users between "I couldn't buy in to Bitcoin because it was congested" and "I bought into Bitcoin but now it's completely stuck because it's congested".
Plus, with L2s like lightning, you need to be able to get your "corrective" transaction on chain within a certain time period, otherwise your channel partner could steal. (You need to get your Penalty transaction in ln-penalty, or update transaction in ln-symmetry confirmed)
I'm pretty sure at least *specifically* with channel factories and timeout trees + lightning, it's not much of a concern, since your channel partner's attempted theft would mean unrolling part of the tree anyway, they actually shoulder most of the fee burden in that scenario, so they have incentive to continue behaving. (Don't take my word on this, I've only half thought it through)
There might be other constructions that create a greater risk though.