Paying bills electonically does NOT mean they're unaffected by USPS slowdowns.

[Klaralven]

19. And even worse, the check arrives at the biller without the bill stub to post the payment

When you mail a check directly to the biller, you usually also return a part of the bill that you received. This stub or remittance advice is the standard way that the biller posts the check payment to your account.

When the biller receives a paper check from a bank, it likely comes with a non-standard remittance advice that the biller may have to process manually to post the proper customer account.

Its even worse if the bank uses "check and list", where the bank sends one check for several customer payments along with a listing of the individual customer accounts being paid. Hopefully this is largely a thing of the past.