This is likely caused by server errors happening within the Templater which could be down to outdated templates or a faulty add-on installation. Mostly when we have seen this, it is down to an add-on.
Interestingly, the last time I saw this, it was related to Siropu Ads Manager which, from the screenshot, you seem to have installed.
So, it will just be a case of narrowing down the external factors and resolving those and that should restore the correct behaviour.