Disappearing Subtitles (stl) in Premiere Pro CC 2018

Hi!

I'm working on an iMac (10.12.6) and since the new update (2018) I have a problem with importing subtitle (stl.)-files.

They were working fine before but now they disappear on the program monitor (while editing) and don't come back.

Even restarting Premiere Pro doesn't solve the problem.

I opened an older project-file and they were back, but after sending the project to the media encoder-queue they disappeared again.

(rendering it out of premiere pro while it is still visible works but if you change anything on the edit the subtitle disappears again...)

Another weird thing is, that when I click on the subtitle-layer in the timeline (after it disappeared on the program monitor), it has no effect-settings anymore.

So there is no way of changing the position/scale/etc. anymore...

I already tried (after the subtitle disappeared):

- importing the project into a new one.

- creating a new sequence by drag&dropping the stl.-file on the "new object"-button.

- opening it on a different iMac (also 10.12.6) and importing the stl again.

but the subtitles are still gone...

I tried importing the subtitle back on Premiere Pro 2017 and it seems to work fine!

Could there be a problem with certain stl-files and the new 2018-update?

Thanks for your help!

Bye

Manuel