Configuration settings not saved - goes to blank page with header and footer.

-- HikaShop version -- : 4.1.0
-- Joomla version -- : 3.9.8
-- PHP version -- : 7.1
-- Browser(s) name and version -- : Chrome / Edge / FireFox - all updated

This is really weird. When I made a change to one of the Configuration settings and clicked 'Save and Close', it went to a page with only the header and footer sections but the changes were not saved. I've downgraded the PHP from 7.2 to 7.1 but the same results.
When I view the page with 'Maximum' error warnings set and inspect the page with developer tools, the 'g-main' has this "404 View not found [name, type, prefix]: redirectonlogin, html, redirectonloginView"

At this point, I am totally baffled why this is happening. Any suggestions?

Nicolas,

I did find that the Redirect on Login plugin was enabled so I disabled it. Cleared the admin cache, went back to HIkaShop Configuration, made the change I needed and clicked Save and Close but got the same 404 page error. I clear the admin cache again, opened HikaShop Configuration, immediately clicked 'Closed' and got the same 404 page error.

So I backed up the site, downloaded HikaShop Business 4.10, reinstalled and tried the same sequence as I did above. Same result.

FYI, error reporting was on Maximum but no messages were displayed.

So I tried this same sequence on MS Edge and FireFox browsers but got the same 404 page.

Then I optimized and repair all tables via phpAdmin and tried again but got the same 404 page.

At this point, I've exhausted my puny brain and clueless what to try next.

Any other ideas?