We love Google Tag Manager and highly recommend using it to install the Mouseflow Tracking Code on your site. One of the main benefits of using GTM with Mouseflow is that it gives you complete control over when, how and for whom the Mouseflow tracking code is run on your site.
If you are having trouble opening the Live Heatmaps it may be caused by GTM preventing them from loading. If you're using a firing rule to make sure that Mouseflow isn't recording yourself and your colleagues this may also block you from opening Live Heatmaps.
Luckily there is an easy workaround to this issue. If you include a firing rule that runs the Mouseflow tracking code when: window.name = "mf_liveHeatmaps_init"
This won't cause you or your colleagues to be recorded by Mouseflow - but it will allow you to open Live Heatmaps.