ForwardRef warnings [V4]

Upgrading code to V4 (from V3), having no issues except for this warning message on a lot of components (but not all):

Warning: Failed prop type: ForwardRef(Grid): prop type component is invalid; it must be a function, usually from the prop-types package, but received undefined.

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior 🤔

No errors

Current Behavior 😯

Get an error for about 40% of Material-UI components used in my application.

Steps to Reproduce 🕹

I have tried to reproduce this in codesandbox but cannot. I also have a hard time reproducing this in my own project. It seems completely arbitrary when it happens. It is not though, as it always happens to the same constructions.

See code:

<Grid container={true} alignItems="stretch" justify="center">
  <Grid item={true}>SomeText</Grid>
  <Grid item={true}><img alt="some image" href="etc" /></Grid>
</Grid>
<Grid container={true} alignItems="stretch" justify="center">
  <Grid item={true} xs={12}>Some item</Grid>
</Grid>

I get the error on the first Grid container, but not on the second Grid container. I have even tried to copy the exact code - only the first gets the error. The other thing all occurrences have in common is that they are all functional components using withStyles. But even then it seems to be a coin flip on which items get the error.

I have tried with both withStyles+createStyles exported from @material-ui/styles as well as @material-ui/core (just in case).

EDIT: Also tried to replace withStyles with the new useStyles. Same error still.

Context 🔦

N/A

Your Environment 🌎

Tech	Version
Material-UI	v4 (latest alpha)
Material-UI styles	v4 (latest alpha)
React	~16.8 (also tried alpha ~16.9)
Browser	Any
TypeScript	Yes

[jwwisgerhof]

As the issue is not related to material-ui, and you have already helped me fix this problem I will close the issue @eps1lon. Thanks again for your help.

[jwwisgerhof]

Both Windows and Ubuntu (WSL). Both had the same issue. New vm was ubuntu (clean image).