GA reporting shows sudden drop indirect traffic

For a few months, our Direct traffic has been increasingly getting higher and higher. Which is very random nothing has changed, no new services etc. Recently we switched from GA embedded code to using GTM and loading in our Analytics script via the tag manager. All seemed to be ok except that the direct traffic dropped overnight from about 2,500 sessions to about 150 sessions. The GTM code implementation looks ok, Google tag assistant confirms that it is installed and running, and by viewing real-time reports I can see my page views. This drop also happened at the time of the GTM code install on the site.

Has anyone experienced an issue like this before?