Null SequencePlayer when trying to play a LevelSequence from BeginPlay in a sublevel

Converted a copy of my project to the 4.17 preview this morning to make sure everything was working correctly and unfortunately I get a crash in one of my maps when it tries to play a level sequence. This issue only seems to happen if your project was converted from 4.16 and the sequence you’re trying to play is in a sublevel.

I was able to repro this with the following steps:

  1. Create a C++ project in 4.16 using the blank template.
  2. Save the default level that is open when the project loads.
  3. Create a new map and add it as a sublevel to the default level.
  4. Create a level sequence add place it in the sublevel. I also added a cube with a track in the sequence that moved it so I could see if it was working.
  5. In the persistent level’s blueprint’s BeginPlay call LoadStreamLevel with your sublevel’s name, Make Visible After Load and Should Block on Load set to true.
  6. In the sublevel’s BeginPlay call Play on your LevelSequence’s SequencePlayer.
  7. Close the project and switch the engine version to 4.17.
  8. Reopen the project and PIE. If you stop PIE you should get an error saying it tried to access None.

I found that if I just set the sequence to auto-play or added a 1 second delay I didn’t run into this issue so it seems like there’s some odd delay with trying to load the sequence or something. Also attaching the repro project I made.

Hey kgamble,

Thanks for reporting this. I’m really not sure why this is happening for your project, but I’ve entered UE-47269 to get it resolved.

It might actually help me a lot if you sent me the 4.16 version of the project so that it can be compared before and after updating. Can you send that along?

-Matt W.

Of course, makes sense that you’d want that. Here it is. I had to recreate it since I didn’t keep a copy of the pre-upgrade around but this at least confirms that I’m able to consistently repro it (I copied this one and converted it to 4.17 to make sure that it has the same problems).