Happened again, and I have not been using the multiload indicator:

[93726.258000] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[112113.785979] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[118349.834605] [drm] nouveau 0000:01:00.0: cal_space: -16
[122716.494874] CPU0: Core temperature above threshold, cpu clock throttled (total events = 116490)
[122716.495358] CPU0: Core temperature/speed normal
[122717.307927] CPU1: Core temperature above threshold, cpu clock throttled (total events = 63861)
[122717.308412] CPU1: Core temperature/speed normal
[122774.816017] [Hardware Error]: Machine check events logged
[123114.666207] CPU1: Core temperature above threshold, cpu clock throttled (total events = 63999)
[123114.666691] CPU1: Core temperature/speed normal
[123114.749191] CPU0: Core temperature above threshold, cpu clock throttled (total events = 116508)
[123114.749676] CPU0: Core temperature/speed normal
[123224.816015] [Hardware Error]: Machine check events logged
[123284.595622] [drm] nouveau 0000:01:00.0: cal_space: -16
[123545.689284] [drm] nouveau 0000:01:00.0: cal_space: -16
[126001.799257] CPU1: Core temperature above threshold, cpu clock throttled (total events = 71191)
[126001.799741] CPU1: Core temperature/speed normal
[126074.816014] [Hardware Error]: Machine check events logged
[126610.271326] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[128729.258426] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[130130.391589] CPU1: Core temperature above threshold, cpu clock throttled (total events = 71193)
[130130.392076] CPU1: Core temperature/speed normal
[130133.216263] CPU0: Core temperature above threshold, cpu clock throttled (total events = 119511)
[130133.216749] CPU0: Core temperature/speed normal
[130200.804021] [Hardware Error]: Machine check events logged
[133260.695861] [drm] nouveau 0000:01:00.0: cal_space: -16
[133260.798452] [drm] nouveau 0000:01:00.0: cal_space: -16
[134660.258223] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[136539.429134] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[144757.223182] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[149860.411640] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[151518.598777] CPU0: Core temperature above threshold, cpu clock throttled (total events = 532160)
[151518.599260] CPU0: Core temperature/speed normal
[152788.253177] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[159358.002143] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[160113.222418] [drm] nouveau 0000:01:00.0: Setting dpms mode 3 on vga encoder (output 0)
[161958.490479] [drm] nouveau 0000:01:00.0: Setting dpms mode 0 on vga encoder (output 0)
[164319.379741] [drm] nouveau 0000:01:00.0: error fencing pushbuf: -16
[165246.132769] CPU0: Core temperature above threshold, cpu clock throttled (total events = 532169)
[165246.133237] CPU0: Core temperature/speed normal
[165397.342368] CPU1: Core temperature above threshold, cpu clock throttled (total events = 415776)
[165397.342852] CPU1: Core temperature/speed normal
[165577.666852] [drm] nouveau 0000:01:00.0: fail pre-validate sync
[165577.666857] [drm] nouveau 0000:01:00.0: validate vram_list
[165577.666877] [drm] nouveau 0000:01:00.0: validate: -16