This was IIRC an issue back in 1990s due to how the system calculated time. So operation of a system continuously for more than 20 hours would cause the system to become ineffective until it was rebooted.
http://www.cs.unc.edu/~smp/COMP205/LECTURES/ERROR/lec23/node...
Thanks in major part to Israel, modern patriot systems have been rigorously tested via fire. To equate the current systems to the ones from 30 years ago is very disingenuous.
Patriot missile batteries in Ukraine have so far successfully intercepted all Khinzal Hyper-sonic Missiles launched by Russia. (At least, the ones that entered their Area of Operation)