If the problem is not because of Dokan why are the other two Dokan pages ok? My Orders and Store Listings pages are fine, this only happens with the Dashboard. It suggests that there is something to do with the css for the dashboard page which causes the problem. Perhaps you could use a different class other than the standard #main or #content or #wrapper etc so that it does not conflict with themes other than your Dokan theme? Just a suggestion
Intial problem which i mentioned still exist actually you have made product width fixed in custom css and now even if i want to show three product in row or if i want to change that it doesn't happen because product width is fixed and if i remove them store single page becomes wierd . Its is the plugin container div which is creating problem.Please check i removed your css for product which you added.
I have removed you css when you add this css all products width becomes 33.33% which you have mentioned important in custom css .So it create problem in selecting 4 products in a row or 2 products in a row cause it is 33.33% always.Also create problem in responsive mode.
We have tried our best to fix that and also provided solution. Now if you can suggest us what kind of fix do you need on that place then we can try. Otherwise you have to hire a developer to customize your theme.