Since migrating from 8.4.4 to 8.5.2 we see this issue (can you re-open it?), it isn't reproducible in test environments, not even in production when requesting the same images. It looks like it has to do with high load and lots of concurrent requests. Errors outputted look like

VipsJpeg: out of order read at line 3016
VipsJpeg: out of order read at line 3016
VipsJpeg: out of order read at line 3016
VipsJpeg: out of order read at line 3016

for ~0.03% of the requests (hence the not reproducible part). Only for JPEG's it seems. Really strange, and we cannot debug it at this time..