(Indexed, though blocked by robots.txt ) warning in Google Search Console

Hi Everyone!

Today I have checked the errors & warning of my site over the google search console where I got a warning in coverage section that some URL appeared with Indexed, though blocked by robots.txt warnings. So my concern is that I have already disallowed those URLs in the robots.txt file and I can't understand why this one is still indexed and warning "Indexed, though blocked by robots.txt". It is appeared over my GSC account .so anyone here who can suggest to me that what should I do something to fix this issue? is it a serious issue or not?

I have also though blocked by robots.txt but my pages are not effected in search console and giving again and again warning some post are indexed by search console and some not indexed. Search console is not indexing my posts. How can Fix this error?