Backup & Restore of marked items
As the game sometimes changes the itemInstanceIds which the addon relies on to save your marker icons, and you are not always using the unique item IDs to save your marker icons (check ingame addon settings -> general settings -> unique item IDs)
you somehow need to have a backup and restore function for your set marker icons.
The following chat commands (and an addon settings menu entry for Backup & restore) are avilable, which you can use before a patch to backup, and after a patch to restore your set marker icons on your items.
!!! Attention !!! Guild banks:
If you want to backup/restore guild bank marker icons you must open each guild bank at least once before you do the backup/restore or the addon is not able to read the data from it. And the guild bank is not static so other users might change it as well after you had opened them.
So the addon is only using the known info at the time you have opened it!
House storages:
If you want to backup/restore your house banks you need to be in one of your houses as you do the backup/restore!
-> So please open the guild banks once and then port into your house to do a full backup/restore!

The backup/restore will use the game's API version [use this command to get it printed into the chat: /script d(GetAPIVersion()) ] to backup to/restore from.
You can specify a different API version if you like to to save it to another value/load from this specified value.
If you do not specify an API version via chat commands the game will use the current version for backup, and the current version for restore. If, e.g. after a patch, the current API version got no backuped data, the addon
automatically will try the last API version for the restore (saved data from before the patch)!

Chat commands:
-Chat command for backup (<...> are optional parameters!)
/fcois backup <withDetails> <apiversion> <doClearBackup>

<withDetails> values: true=show each backuped item in chat/false: do not show any backuped item in chat
<apiversion> value:nnnnnn=6digit game API version which you can specify to save the backup with this apiversion. If not specified the current apiversion of the game is used
<doClearBackup> values: true=clear the specified apiversion backup before a new one is started/false=do not clear and keep old backupdata of thespecified api version

-Chat command for restore (<...> are optional parameters!)
/fcois restore <withDetails> <apiversion>
<withDetails> values: true=show each restored item in chat/false: do not show any restored item in chat
<apiversion> value:nnnnnn=6digit game API version which you can specify to load the backup from. If not specified the current apiversion of the game is used and if there is no backupdata for the current apiversion the last apiversion will be checked (e.g. after a patch the apiversion raised and your backup got the last apiversion saved -> the addon will automatically find it then)

Where are the backups saved:
Backups are saved to the SavedVariables (depends on your current save type: account, char, all accounts the same, all servers and accounts the same) subtable "backupData", and then with another subtable of the APIversion you have run the backup with.