Both are x264 encoder crashes. On one of my systems this happened a few days ago.
Same CPU as yours, same calling sequence, same OBS version, same Win 10 build, although different revision.
Safe to say, there is an out of exception being triggered and its not always reproducible. Welcome to the club.
Unhandled exception: c0000005
Date/Time: 2018-02-10, 20:43:45
Fault address: 7FFF282E36D2 (c:\program files (x86)\obs-studio\bin\64bit\libx264-148.dll)
libobs version: 21.0.1
Windows version: 10.0 build 16299 (revision: 192; 64-bit)
CPU: AMD Ryzen 7 1700X Eight-Core Processor
Thread 308C (Crashed)
Stack EIP Arg0 Arg1 Arg2 Arg3 Address
000000BC3335EDB0 00007FFF282E36D2 0000029CAFDE7220 0000000000000000 000000BC3335F7C0 0000000000000004 libx264-148.dll!0x7fff282e36d2
000000BC3335F6D0 00007FFF282C07A5 0000000000000000 000000BC33755DC0 000000BC33755DD0 0000029CA73B1860 libx264-148.dll!0x7fff282c07a5
000000BC3335FB00 00007FFF282C029A 0000F269D90BB57A 0000000000000000 0000000000000000 00007FFF69F4A41A libx264-148.dll!0x7fff282c029a
000000BC3335FB90 00007FFF283139AD 0000029CB1E9D560 0000000000000000 0000000000000000 0000000000000000 libx264-148.dll!0x7fff283139ad
000000BC3335FBE0 00007FFF28313DA5 0000029C922D2100 0000000000000000 0000000000000000 0000000000000000 libx264-148.dll!0x7fff28313da5
000000BC3335FC10 00007FFF69F4A8E6 00007FFF69F9F6E0 0000029CB1E9D560 0000000000000000 0000000000000000 msvcrt.dll!0x7fff69f4a8e6
000000BC3335FC40 00007FFF69F4A9BC 0000000000000000 0000000000000000 0000000000000000 0000000000000000 msvcrt.dll!0x7fff69f4a9bc
000000BC3335FC70 00007FFF6C401FE4 0000000000000000 0000000000000000 0000000000000000 0000000000000000 kernel32.dll!0x7fff6c401fe4
000000BC3335FCA0 00007FFF6C6BEFB1 0000000000000000 0000000000000000 0000000000000000 0000000000000000 ntdll.dll!0x7fff6c6befb1
