Blueprint internal compiler error after undo

I’ve run into what I think is a bug when attempting to compile a blueprint after mistakenly breaking a pin link and then hitting Ctrl+Z to undo. It’s only happening in one pair of nodes in a particular blueprint, but they work fine beforehand and when recreating them manually after the error. Searching the hub shows a few other people with related issues, but the reports are either very old or were caused by scripting oversights, where this issue consistently appears and doesn’t seem related to my game logic.

This is happening in a binary build of UE 4.10.4, from the launcher, specifically version 4.10.4-2872498, but I’ve just tested 4.11 Preview 7, version 4.11.0-2896623 (also binary through the launcher), and found the same behavior.

Using the attached project, I can reproduce the error message every time I follow these steps:

1.) Open BPError410.uproject in Unreal Editor 4.10.4-2872498.

2.) In the Content Browser, enable the Sources panel, select the Blueprints folder and open the SideScrollerCharacter blueprint.

3.) In the Blueprint editor, click Compile to confirm that the blueprint compiles correctly before making any changes.

4.) Open the Event Graph tab and pan to the right until you find the “Volleyball Set” node. Underneath it should be a Get node for a variable named “Current Ball”. Alt+Click the wire connecting those nodes to delete it, then click Compile and see that an error is thrown regarding the missing connection, as expected.

5.) Hit Ctrl+Z to undo. The bottom right corner of the UE interface should show an “Undo: Break Pin Links” popup, and the “Current Ball” Get node should have its output pin filled in with solid blue once again. The wire, however, is still gone, and the input pin for “Volleyball Set” remains hollow.

6.) Drag from the output of “Current Ball” to the input Target pin of “Volleyball Set” to reconnect them, then try to compile the blueprint. The Compiler Results tab should list a series of errors, among them “Internal compiler error inside CreateExecutionSchedule (site 1); there is an issue with node/pin manipulation that was performed in this graph, please contact the Blueprints team!” and a series related to “ICE SetVariableOnPersistentFrame”.

7.) Delete the “Current Ball” Get node and replace it with a new one, connect the pins and recompile. The compile should finish with no errors.

At this point you can repeat steps 4 through 7 to introduce and resolve the error as many times as you’d like.

Since the error vanishes when I recreate the Get node, this isn’t a major issue for me, and I can keep working on my project without a problem. The error message did explicitly ask me to get in touch with the Blueprints team, though, so here I am. I hope this helps, but if you need more details I’ll help however I can!

Hi ItEndsWithTens,

Thank you for the report and the thorough repro steps with the test project!

I was easily able to reproduce the issue and I’ve created JIRA UE-28440. Our developers will be investigating further.



You’re most welcome, thanks for taking a look at it! Gives me peace of mind to know I’m not just doing something stupid.