I've just got a similar issue. I updated a site from MODX 2.2.* to 2.7.0 going step by step through all minor versions but skipping patches. This update caused 2 problems:
1. News and Security feeds didn't show any data except the loading message
2. Package manager wasn't able to load a list of packages and displayed the loading message as well.
After some debugging it turned out that the first problem was caused by a missing locale setting. A default locale on my server caused feed processors to generate text with broken UTF-8 characters (apparently, they were produced by the strftime function). MODX wasn't able to encode it as JSON and returned an empty body instead of the expected response. An interesting thing is that neither success nor error handler was triggered by such response on the client side.
This problem was solved by specifying a correct local in settings: System Settings > Lexicon and Language > Locale.
It looks like it solved a problem with the package manager as well.
I think the problem with the feeds is also breaking UpgradeMODX and preventing it from getting the version list from GitHub.
Turning them off, then back on, manually clearing the cache, and moving the UGM widget above the feed widgets solved it for me (so far).