I recently tried to upgrade a Nopcommerce 3.4 site to 3.6 and had some issues. After I ran the upgrade scripts, the upgraded site came up, but had multiple customer roles for the system roles. Administrator was duplicated about 10 times, and the guest roll had a couple dozen repeats. You can not delete duplicate system roles inside of nopcommerce, so to fix would require directly making changes on the database. NOT GOOD. After looking at a similar issue posted on the nop forum, I can be fairly certain that the cause of this was due to plug-ins. I do have a couple other plug-ins installed that are not NOP-Templates, however I wanted to check to see if it is recommended to uninstall all plugins BEFORE doing a nop upgrade on a live site. This certainly adds to the pain of performing an upgrade!
I can assure you that this is not caused by our plugins. Otherwise our forum would have been flooded with similar complaints.
The best way to upgrade nopCommerce is this one:
1. Back-up your existing database.
2. Copy the InstalledPlugins.txt and Settings.txt.
3. Download the desired version of nopCommerce and place it any folder.
4. Paste the InstalledPlugins.txt and Settings.txt into the new folder of nop.
5. Go to our site and download our plugins for the desired version, then place them in the new nopCommerce folder.
6. For each "mid-version" run the nopCommerce upgrade script, then run ours if there is one.
Example: You upgrade from 3.40 to 3.60. So, for 3.50 run nopCommerce upgrade script, then run ours. After that - for 3.60 run nopCommerce upgrade script, then run ours.
7. Now, if you start nopCommerce everything should work fine.
You do not need to remove/uninstall any of the plugins.
For test purposes you can back-up your database, then uninstall and remove all the plugins (not only ours) and try to upgrade the database. Then you can check how many records you have into the CustomerRoles table.
I hope this helped !