My guess is Content Manager is validating content. TS12 used to do this quite often which would freeze things up for quite sometime. To see if CM is validating content you need to enable the database processes console windows.
When you start up TS12, click on options at the launcher.
Go to the developer tab and check show database process windows.
When you start up Content Manager, small command prompts will appear on the taskbar. Click on these and you'll see stuff in there, usually a bunch of numbers and log in information. What will stand out is validating content. This will say something like validating asset (some kuid number) xxxx, where xxxx= some number. As each and every installed asset is checked, this number will decrease. When the number reaches around 33 or so, it won't go further and you'll be done validating.
This explains why it you have the freeze ups while online only. The program is checking your install against the master database.
Now there are sometimes other issues which can cause this such as that stuff in the queue. When and if CM stops and unfreezes, see if you can clear the queue. At this point, I highly recommend running a quick database repair.
Click on File menu.
Click on Quick Database repair.
Note: A "Quick" database repair can and will take a lot of time, depending upon the amount of content you have installed. This is a quick, or cursory, check of the data and not a quick pass on the database to do the job quickly.
When the process is complete, check for faulty assets. This process can and will produce false errors. Clear the errors by write-clicking and viewing errors and warnings. If there are any remaining errors, you need to repair or replace that content.
One additional thing which needs mentioning. We do highly recommend submitting that content you have there which is open for edit. Having lots of open for edit content like that can cause performance problems as well, which maybe contributing to the problem you are having now.