UnknownGadgetException: No gadget template was found for the template id = 000b5e2a-6a31-4b1c-adaa-b074619de55b
Is this error coming on your local environment or on PROD environment ?
If you are using "CMS 6" with loadbalancer then this is known bug-
A workaround to fix this by "enabling "sticky ip" on the load balancer.
Could you please provide more information like Episerver version, any external addons etc... so that someone can help.