it took me three tries to get my SP3 to finish the install.
Initial Check = OK
Download of AU = OK
Installation = would start the process; but then I got a "something went wrong" message; Options were: Retry; Cancel; Contact Msft Support. I hit Retry; it went through the whole download process again (but much quicker), and again the "something went wrong" message reappeared while trying to install. I had to do this three times for the install to take; but, everything seems right as rain on; my SP3.