Mobility is changed on BP, breaking all instances

Hi,

We have an issue where Mobility is changed sometimes on BPs, which causes all instances of that BP to be placed in origin, due to the root component changing mobility from Static to Movable and it has components under it that are static.

We don’t have a clear repro, in fact it happens quite rarely, but when it happens it can ruin a lot of instances. It’s always triggered by some change to the BPs themselves and the Mobility flag is changed on the BP, thus the instances break.

Our BP setup

Base_BP

Inherits from Actor

Has a Scenecomponent as root component, the Mobility is set to Static.

There are also several static mesh components under the root component. Some are Static some are Movable

Child_BP

Inherits from Base_BP

This BP has no change to the root components Mobility flag.

It shows up as Static, it has the revert arrow on it and clicking it will reset it to Static (I would expect it to reset to the value in Base_BP)

Child2_BP

Inherits from Child_BP

This BP has no change to the root components Mobility flag.

It shows up as Static, there is no revert arrow to click here.

It’s this BP that sometimes when people edit it, it will change the root components Mobility to Movable

We don’t have any more information about this or what changes causes this to happens. It feels very random and we have been unable to try and isolate or reproduce this issue.

These BPs have gone through several changes by different people, including some bigger refactors (very possible we have changed the inheritance on them through their lifetime).

Anything you have seen before? Any ideas on what could cause this to happen or for potential fixes?

Best Regards

/Roger

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Hello! I’m reminded of this bug UE-163285 which is specific to if Base_BP’s root component is the default existing DefaultSceneRoot. Is that the case in your setup? If so, we haven’t fixed UE-163285 but replacing DefaultSceneRoot with a manually added SceneComponent should be a reliable workaround for the problem.

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Nice! That should fix your issues. I’ll close this but if you still encounter problems, do let us know.

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Indeed it is, we’ll try this. Thanks!

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