Hi, maybe use the most basic fix: Template Options > Advanced > Compile SCSS to CSS : OFF > Save

If I were to do this I loose some of pages content (I've tried this already). I need to find a permanent fix, not a temporary patch.

Video guide was quite simple, but I guess not for all webmasters. Don't worry, please download a file, unzip and replace on your server templates/shaper_revibe/less/theme.less

http://www.filedropper.com/theme_2

Thank you for the file. I replaced the existing theme.less, deleted cache, however I'm getting the same error.

For the time being I disabled compilation of LESS to CSS (Compile LESS to CSS -> OFF), since I need the site to be up and running. However, like I've mentioned already, I hope you can provide a permanent solution so I won't loose any of site's content.

I found a culprit of my issue - there were 4 instances in theme.less file of a non-existing variable - .border-radius. Once I removed it and reenabled compilation of LESS to CSS, my site no longer generates the same error, however now I'm running into a new issue - my custom module which was supposed to be in the top3 position no longer displays. Any idea why?

It's not realeated with main issue. Check on Template Layout if this position still exist.

Without URL + access etc. I cannot help more

I did check template layout and this position still exists and all of it's settings look good to me. I need your email to set you up with access to the website.

Is anyone available to help troubleshooting the issue?

use random e-mail, I need account for few hours.

ok, I created user for your access. How can I send you ID/pswd info?

Use "Hidden Content" field. Below classic answer. I will check tomorrow, now is late hour for me.

btw, it seems that all of Menu URLs no longer work either.

Here is your site access info.

it seems that all of Menu URLs no longer work either.

But 404 is not from changes in CSS! No joke. Let's be serious. Maybe you edited .htaccess, for example by changing PHP version. Or changed settings in sh404sef.

BTW

1. Your Joomla asking you to update 9 extensions.
2. Using plugins like System - jQuery Easy - can cause unexpected problems. Joomla have its own jQuery.

I hate to say it, but I was right. Your file .htaccess was overridden by cPanel or ??? extra extension etc. For sure not by me, nor Joomla itself, nor our software. Anyway, I fixed it. No 404 error anymore. You're welcome.

About X-file case with missing Custom module on the position "top3" - I see it. Yes, this module is displayed. Here is evidence (screenshot): https://ibb.co/945mpd7

Thank you very much for your help! I have no idea how possibly .htaccess file got messed up. Very odd... I can see now custom module on the position "top3" in Microsoft Edge, but it does not work for me for some reason in Chrome, even after I cleared site's and brower's cache.