Restarting Chrome didn't work for me but I might have a workaround.
Submit / save the post with non-working images.
Close browser.
Re-open browser.
Go to thread and edit the post in Advanced mode.
Double click the troublesome image in the edit area.
Select image Size of Medium.
Click the Preview post button.
Click on the now medium sized image in preview area. (For me it then opens the larger image.)
Double click the image in the edit area.
Change the image size to Thumbnail.
Click the Preview post button.
Click on the thumbnail in preview area. (Once again, for me it then opens the larger image.)
Save the edit.
I'm not certain that all these stages are required but it's worked for me twice in a row. It's entirely possible that this is merely coincidence and stripping naked, daubing myself in fermented marmoset scat, facing West Sou' West and reciting an ode to the goddess Tharga in pig Latin would have been as effective. However, if you find either technique to work consistently do please confirm as much in a post. Ta.