If you are using a plugin similar to WP RSS Aggregator, the issue is within the image parameters of the plugin itself. There should be an image parameter setting within the aggregator, assuming you are using the plugin’s premium plan.
The way we get around aggregator image issues, is there should be a setting to use a standard feature image for each feed, which only shows about at 1% visitor engagement loss.
All aggregators are fairly archaic, so the solution may not present itself easily.