There seems to be some problems with jobrunner recently (see comments from T7626#157135), but this is unrelated to that task. The jobrunner application logs on each mediawiki server indicate that this problem is caused by a segmentation fault.
Full details are a bit hard to determine, but it appears that this is error 14: attempt to execute code from an unmapped area.
For purposes of debugging, the error from the kernel log appears in the format of:
segfault at 7fXXXXXXXb80 ip 00007fXXXXXXXb80 sp 00007fXXXXXfea08 error 14
(I've kept everything that is the same between each entry)
Some also come with a bit more information, such as: