Bug introduced in V10.4 or earlier, fixed in 11.1.0
A support case with the identification [CASE:3710168] was created.
[...] I was able to reproduce the issue [...] I am checking with the development team to see if we have a workaround for this.
DynamicUpdating off and on, the
UpdateInterval option displays
Dynamic[RandomReal, UpdateInterval -> 1] x = 1; Dynamic[x] Slider @ Dynamic[x] Checkbox @ Dynamic @ CurrentValue[EvaluationNotebook, DynamicUpdating]
Worth to mention that if this notebook is saved in an untrusted path, opened and is asking to
"Enable Dynamic Updating" then it works fine.
Also, toggling with Evaluation/DynamicUpdatingEnabled menu item works fine.
It makes the answer to Create a notebook and save it without prompting Dynamics partially unusable.