The jquery.client module currently treats Windows 10's new 'Edge' browser (aka Project Spartan) as MSIE 12; this causes some trouble with versionless UA-sniffing code that assumes MSIE will never improve.
Microsoft has actually gone to some trouble to make Edge's UA string detect as a WebKit or Gecko-based browser to avoid those sorts of old hack checks, but our conflation is bringing them back in MediaWiki JS code -- for example T97901.
It may be wise to have the module treat Edge as a separate browser, reporting it as 'edge' or 'msedge' rather than 'msie', so any other old code checking for 'msie' doesn't explode on Edge.
Any further issues we find where Edge is broken should be reported to Microsoft; their dev team is much more open and responsive than they used to be. (Note that David Storey formerly of Opera is on the Edge team now, he's contacted us about a few issues and has been very responsive.)