However, this issue is not critical, and there are solutions for this error.
Deactivate themes that are damaged
Maybe one of the themes on the website is creating the error. To check which theme is disturbing, deactivate one by one and then check the website. Activate them one by one after that and find the real culprit.
Disable plugins
Your website plugins can also create this error, so do the same procedure with plugins and disable them.
Contact Host provider
Contact the hosting provider and ensure that the problem is not occurring from his side. If it is from the host side, then, the hosting provider will provide the solution to this error.