How to sync messages and preference sidebar issues on Mac

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Then have a few suggestions ;

Start now and open an Apple Support Ticket as they are PAID  Apple Employees to deal will these types of issues . 

1 800 MyApple

Other location call Centres 

 Contact Apple for support and service

8313laura wrote:

Both my iPhone and iPad are not having any issues with syncing and deleting messages This is only happening on my MAC What follows is related to my MAC.

1) In my troubleshooting I accessed iCloud.com only to find that it does not show the messages app ( and an app cannot be added from there).

2) I cannot follow the instructions to "setup iCloud for messages on my Mac" because when I try to go to settings/preferences/messages - The word "messages" is not shown in the sidebar ( nor iMessage) so I cannot access from here.

3) Next I went to my applications. When I left or right click on the messages icon the only thing that is visible is the text messages I have sent or received.i do not see iMessage or anything else.

All that has been done appears to have been done on an iPhone to iPad

Correct ?

The instructions supplied are to be done on the Apple Computer

Keep your messages up to date with iCloud

Set up iCloud for Messages on all your devices