None of what you describe shows up in my iMovie 10.1.12. I don't get "theme:no theme" under "Titles". All of my titles are displayed with every project, and I don't get an "A" symbol next to the project title in the project browser screen. So I can't replicate your issue on my computer or do any testing.
Try clicking on the Settings button located above and to the right of the timeline, and unchecking the box that says "Automatic Content". See if that makes any difference.
Also, you can add additional lines of text to a title by holding down the Option key as you press the return key on your keyboard when you reach the end of a line.
When you create a brand new project, if all of your titles show up, try going back to your original project and do an Edit//Select All, Edit/Copy, of the media in the project and then Edit/Paste it into the newly created project. Now see if all of your titles continue to be displayed.
You might benefit from talking to the savvy techs at Apple Support. They have the capability of remotely accessing your computer that we don't have here. Click on the Contact Support item in the upper left right hand corner of this forum's screen and navigate to a place where you can enter your phone number.
At this point I am out of ideas. It might be a glitch in the new iMovie version. If the support people come up with something, please post back if you have time.
-- Rich