Alex,
It looks like you are not using the problemIdentifierPrefix feature of the iframe API. If you insert the number of the problem in there it avoid the problem you are seeing. I remember putting this in specifically to allow the exact same problem file to be used several times in an HTML page.
< iframe width="800" height="400" src="https://demo.webwork.rochester.edu/webwork2/html2xml?
&answersSubmitted=0&
&sourceFilePath=Library/Union/setSeriesTaylor/ur_sr_9_6.pg&
&problemSeed=123567&
&courseID=daemon_course& &userID=daemon&
&course_password=daemon& &showSummary=1&
&displayMode=MathJax& &problemIdentifierPrefix=102&
&language=en& &outputformat=sticky">
<
/iframe>