There's no particular reason why.  It's not supposed to happen.  Your entries are continually saved to the cloud but when something goes wrong, you should see a message popping up to tell you there is some sort of connection problem, etc.

To ensure you don't run into problems using PTO, you should use only a PTO-supported browser and preferably in incognito mode. 

Before going back into PTO, you may like to do the following:

• Clear cache and cookies (and I'd also do history);
• Restart browser; and
• Restart computer/device.

If this problem persists, send the return to Support from within PTO and give them a call.