Failed to include Tag Manager data

When in Site Settings -> General I include the data of the Goolge Tag Manager of dimafe.es GTM-K5LMCMD the behavior when opening the web is very strange. First of all, letters appear that appear very quickly and it takes about 3 seconds for the web to appear.
The dimafe.es website does not have the tag manager data included, but the robotica.dimafe.es website is a subdomain if it has one. You can check the difference that exists when presenting the web.
The template is the same, the only difference is the inclusion of this data in the web robotica.dimafe.es