Almost 700 of KFC's 900 UK outlets have reopened following a chicken supply fiasco that began about a week ago and forced many stores to shut their doors.
However, the fast-food chain has not said how many are serving a full menu.
KFC said on Wednesday that some would remain closed for the rest of the week, while others will have shortened hours.
The closures followed KFC's decision to switch suppliers from Bidvest to DHL, which is using a single warehouse near Rugby for deliveries nationwide.
DHL has blamed "operational issues" for the supply disruption from the purpose-built facility.
KFC said more chicken deliveries would be be made to outlets on Thursday as teams "continue to work flat out all hours to clear the backlog caused by the breakdown in the DHL distribution system".
DHL has apologised for the "inconvenience and disappointment caused to KFC and their customers" and said it aimed to restore normal service levels as soon as possible.
The GMB union has criticised KFC's decision to move its contract from Bidvest, which national officer Mick Rix said was a "very well respected, specialised logistics provider", to one that lacked a track record in food distribution.
The union has also claimed some KFC workers were being asked to take holiday while stores have been closed.
A KFC spokesperson told Personnel Today: "From the information we have been given, nine out of 10 (in 708 of 780 restaurants) of our team members will not be financially worse off this week than they would have been if we were fully operational.
"While not perfect, the remaining 10% are ensuring that they do everything possible to provide hours or take paid leave."
Four in five of KFC's UK outlets are run by franchisees, meaning the company has no direct control over them.