Works for me on several different browsers and an android phone. Don't forget to clear browser caches as well as Joomla caches.
By 'comment' field you do mean the 'Nachricht' (message) field?
Simple ("Conservative") Caching of Components will be blocked/deactivated/doesn't work when Plugin "System - RSForm! Pro Delete Submissions" is enabled.
Steps to reproduce/test :
Activate the Plugin
Turn on Simple( so called "conservateve" ) Caching in Global Settings -> Tab "System" -> set "Cache" to "ON - Normal Caching" ( versus the next option, which is called "progressive" )
Call an article in the frontend ( makes sure you're not logged in in frontend btw.! )
The first thing you should try is to match the form's layout against your template framework. More precisely, please navigate to backend > Components > RSForm!Pro > Manage Forms > your form > Properties > Form Layout > Choose a layout that matches your template. If you're using cache, clear your Joomla! installation cache and check this once more (it may also be required that you properly refresh your form's page in the frontend area using CTRL+F5).
You're most likely experiencing a caching issue. This article explains why a form might not work correctly with cache and what to do.
To test if this is a caching issue, temporarily disable your Joomla! caching, then clear it (you'll need to clear it as well) and test the form once more.