You don't say which version of Clarity this is with, if it is 12.1.2 or lower, then I suspect it is this defect:
CLRT-14821 LOG[bg-niku]: Error: NAMESPACE_ERR: An attempt is made to create or change an object in a way which is incorrect with regard to namespaces.
Ignore the fact it says 'bg' and not 'app', that is just due to the original location it was found and reported, but I've seen this appear in both regardless. It's a strange defect, it strikes almost without warning, and can be quite persistent once it decides to surface in a part of the application, until you restart it and then it goes away (in most cases, seemingly 'forever', as it is rare to recur).
Fixes for it were introduced into Clarity 12.1.3 and 13.0.0 so that it wouldn't happen again, but until you're on those versions or higher, the only recourse is to restart the affected service and then try again.