Can you clarify are these embedded videos or player based videos?   Im guessing embedded? If they are i really recommend the plugin  YouTube Playback You will find often the embed preload would be skipped and in that case the link after click if finally available. things like pause , re plat etc can...

Since you dont have target then you will need either to have   1 devs custom code some banner to geo location based logic 2 use a banner serving tool that does allow geo location       

You would need to perform tests on purchases to ensure you are not dropping any orders.   Did you do a QA of changes and actually test/verify purchases and all related metrics? 

If redesign has caused this to be sure look at things like referring domains, did you lose alot of bookmark and search engine traffic?   Perhaps missing pages need a better redirection strategy if not done so. now

In your case the CRM you use. Is there any credits, cancellations occurring that could also help cause the gap?   Also do a check if there are orders missing from your CRM side is it a few customers only or many different? Can be some IT dept for them have settings that block some analytics tags fro...

Yah check is there a geo IP city/region/country spike on the page?

If your analytics setup tracks tracking IDs then correlate the page against IDs to see if one in particualr is a spiker   Penetration testing can be performed to simulate thousands hundreds of thousands of users. Its an IT function so you need to inquire internally with whomever manages your network...

Check if:   UVs relate to a spike with a particular page Is there and tracking IDs that also spike(perhaps marketing did a social buy?) look at any referring domains that may have spiked Did your IT team try any penetration test    

I would check  IT penetration testing or network blocking happening? Odd how its Microsoft related browser that is tanking the most.   Do most of your customers come from any IT group that maybe has strict Windows security browser settings?