The problem the large travel companies face is that in normal times the booking process is largely automated. Hotels are contracted and flight programs are drawn up months in advance. In a normal season there might be some disruption due to unforeseen events in a particular destination or minor changes to the flying program but overall the changes are minor when compared to the scale of the operation. With lockdown most of these businesses were forced to close down their customer service centres at a time when thousands or even millions of flights were being cancelled. This resulted in a huge amount of customer dissatisfaction as people tried to find out what was happening or obtain refunds. As we move through this crisis companies have been able to reopen their customer service centres and increase the number of agents but there is still a far greater demand for assistance than in a normal season.
As the companies get on top of the refund situation and operations restart there will be further problems. Not all countries will reopen, nor will some hotels and not all flights will operate. At the moment the situation changes on a daily basis. Therefore, many customers will need to be contacted to see if they are happy with the changes or wish to re-book or cancel. This will be very time consuming and I would assume it will be dealt in date order. Hopefully, as time progresses there will be more certainty.