A whole bunch of things,
They didn't order the buds or w/e they are called (wireless ear bud - airpod competition product) but thought they did and promoted them, presold them, etc. so ppl showed up to the store and were like "where are the buds I pre ordered?" and yeah they were no where to be found because there was an error high up the chain with purchasing them and all of that
Also a lot of errors with the storage on the S10s themselves - like the amount of phones they pre sold that were 128g , 512 g, and 1tb storage were all mixed up so people who paid for a 1TB phone showed up and the stores were like "well actually we don't have any left... but we can give you this one that has 1/2 or 1/10 the storage!" and vice versa "oh we don't have that one but if you pay x hundred more dollars you can have the 1TB model..."
etc.
Best Buy rly screwed up apparently