How big are these images? Not in terms of filesize, but in actual image resolution?
Large images require more memory to process. Are these images particularly large?
Is there anything else unusual about them? Are they black and white?
Also try:
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
–
resetting the plugins folder by FTP.
– switching to the unedited default Theme (Twenty Sixteen, etc.) for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins).