I'm going to chime in here as the conversation has already started from which I want to reference a few items.
While Sean is correct that there is a redirect on page load, - which is weird & not likely optimal - the redirect isn't causing the UTM parameters to be dropped here.
If you check the Network tab of the debug console of Chrome you'll see the two requests for the URI you listed above. If you click the requested file (in the network tab) & navigate to the 'Headers' tab you will see that Query String Parameters are still there & being passed.
Now let's circle back to the original problem & see if we can't get to the bottom of it!
I checked out the graph you linked and while it does seem that there's an inverse correlation there, I wouldn't assume too quickly that they switched. I would encourage you to dive into the data a little bit more. Specifically:
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I would use Google Search Console's Search Analytics (the actual interface, not the section in Google Analytics) & look to see if the number of clicks around that same time changed much.
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If there is a noticeable change, dive into the keywords & Landing Pages that saw the shift
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If there is not a noticeable change, we can cross an actual organic change off our list.
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I would also look at the change over that period in GA's landing page report. Look to see if there are any pages that saw a gain/loss over the period in question.
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If there is, add a secondary dimension of medium & see where the change lies
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If not, mark it off
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The final door I would check is the changes that were made for remarketing
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What if any changes were made within Google Analytics? Specifically the admin portion, while I'd check all changes you may have made here, I'm specifically curious if you may have added the URL Query Parameters as exclusions?
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Were any tags, tracking codes, etc added during this time & are the implementations correct?
If you dive into these and summarize your findings here, I'll be more than happy to help you further. Though, I have a hunch that the answer is behind one of these doors.
Good luck!
Trenton