So the issue is likely related to your style (or any edits you have made to it) or another add-on (do you use another media sites add-on?) or changes you may have made to the Instragram media site in the ACP.
No idea that the issue is so you'll have to test in a completely default unedited style with all add-ons disabled to see if the issue still occurs. If it doesn't, then enable these one-by-one until you find the culprit.