Which would indicate that my system is not overclocked
Your log file suggests otherwise:
arm_freq=1000
sdram_freq=500
core_freq=500
Are you using pi2 or pi3?
Default arm_freq for pi2 is 900, core_freq is 250.
For pi3 default value for arm_freq is 1200, core_freq is 400.
Also from your log file:
18:53:01.854 T:1961745360 NOTICE: ARM mem: 864MB GPU mem: 160MB MPG2:0 WVC1:0
160 mb for GPU mem is too low. This will cause issues with HEVC decoding. You definitely need to add or edit the gpu_mem_1024 value in config.txt.
Update: I just tested with gpu_mem_1024=160 on my pi3. With that setting Kodi crashes immediately after I start the playback of a HEVC file.