As per title. The only thing I can find after much searching is that it's because Steam hasn't been shut down correctly. I do shut it down correctly though.
Same here runs fine. It could be its not closing down properly when Windows closes. I had this under Windows 7 for ages. Do you have steam cloud sync on for your games by any chance ?
I've got Steam installed on 3 computers and they all do this verification thing when they load as Windows starts up. Mixture of W7 and W10. All are cleanly shutdown as well.
It is a version check as already mentioned. Surely no biggie in the time it takes on any half decent gaming PC surely?
tbh, manually shutting down steam every time you shut down the pc is probably more hassle than just ignoring that window the the 10 seconds it appears.
Maybe because Valve are fed up with people running a dodgy Steam version which uses spoofing to convince Steam its running paid for legit games! Hackers found a way about 5 years ago to install NIC system drivers at an admin level which tricked Steam into not properly checking the integrity of games by redirecting the IP traffic back to the loopback address 127.0.0.1 instead of back to Valve.