Tested the issue in Android and able to reproduce the issue. Similar behavior is observed since Chrome #65.0.3325.88

Prerequisites: Enable "Simplified View" from Chrome Settings >> Accessibility.

Steps Followed:
1. Launched the Chrome Browser.
2. Navigate to the URL: m.frazpc.pl
3. Tap on any of the article. 
4. Scroll the page up and down.
5. Tap on any "Show simplified view" option.
6. Observed that, simplified view is displayed.
7. In the same tab's omnibox, enter chip.pl and navigate to the respective page.
8. Tap on device back button.
9. Observed that normal view is displayed instead of  simplified view.

Chrome versions tested:
65.0.3325.88(Beta), 66.0.3356.0(Canary)

OS:
Android 7.0.0

Android Devices:
Samsung J7

This seems to be a Non-Regression issue as same behavior is seen since M65.  Untriaged for further input's on this issue.

Please navigate to below link for log's and video--
go/chrome-androidlogs/816870

Note: 
1. This issue is not observed in Desktop.
2. Builds before M-65 doesn't have Simplified View option. Hence Untriaged this issue.

Thanks!

+wychen@ and mdjones@ for further investigation.

WAI: This is the intended behavior. The back button should bring the user back to the original, unmodified site.

Please read #0 - "Show simplified view" is not offered, when frazpc.pl wasn't opened in tab. 

You need to open it, go into other site, back and then "Show simplified view" is visible.

I thought that it's clear.