Some have simply cancelled all new registrations until further notice. Others simply don't respond to queries (waiting over 10 days).
I understand that there is clearly a backlog but I have business to do.....
I'll have a look at the smaller ones you mentioned. Have you experience of any of them? What are their rates like? Would you be uneasy in transacting a large amount through them?
And this happens everytime their is a high percentage on the increase of bitcoin. Many people would withdraw their profit during that increase. But for me, i sacrifice some transaction fee for my transaction to be prioritized to at least 2 hours and waiting on bittrex.com . Normally the clog would at least diminished as the price becomes stable. So try at least waiting longer to withdraw.