Some things to try and confirm.
Does the passed variable Brush have type Texture2D?
Try setting without Match Size checked, maybe something weird is happening there.
It’s possible you have set the texture correctly but there is a size/scaling issue. If match size is true and the texture size is very small, it may be hard to see a change.
I recommend checking Tile_Image properties to see if there is something gone awry there, maybe image alpha is set to zero, texture size is zero, Draw As is set to None etc.
Worth double checking those kinds of values.
Another thing to try is to set up a test with the tile widget in isolation. If you can update a single tile widget’s image texture correctly, then there may be an issue with the container or how you are calling SetTileBrush.