I can't comment on your specific situation @Helen0 and in my area we haven't started the change process to host-only fees yet.
But in theory, if your prices were correctly adjusted, there should be little impact.
Airbnb started displaying total prices for all listings well before this change, so guests saw an all-inclusive price anyway. The change affects where the service fee is collected, but the total price was displayed all along.
The guest service fee used to be "up to" 14.2% (and host portion exactly 3%, both excluding VAT) where the total single host fee is now 15.5% excluding VAT. So - because the guest fee wasn't the same everywhere- there can definitely be a change in total price. But it shouldn't be so significant that bookings dry up.
I don't know what's causing the slowdown for you, but I don't think you should blame yourself for changing early.