I think umbrella projects are not popular because very few people understand what they are, how to use them and why use them.
On top of that, there multiple issues mentioned here and elsewhere about troubles with tools, dependencies, testing etc.
Official docs just tell you to create an umbrella project without telling you any of the reasons why. (Well, some description it’s tacked to the end of the previous section, “Internal dependencies”).
So, back to your question:
What issues have people had that has put them off Umbrella Projects?
Most people never even started with umbrella projects because they are an unknown.
