In my case, the problem with iCloud silently refusing to accept incoming Gmail appears to have been fixed -- a thank-you to Apple support! I have another similar problem that's continuing: iCloud is still silently refusing to accept or deliver incoming mail from a real estate website to which I subscribe. Indulge me for a paragraph, because it leads to a larger point.
Those updates used to be delivered to my iCloud email account. As with the now-fixed Gmail problem, those blocked emails don’t go into the junk folder —they’re blocked from delivery entirely. When I checked my subscription settings on the website they were fine, and I added a cc: to a different email address. That Comcast account gets the email, and the headings indicate the messages are still being sent to my iCloud account, even though iCloud is not letting them through.
Over the years, including in the MobileMe incarnation of Apple’s email service, I’ve had problems with Apple silently blocking email — sometimes incoming, sometimes outgoing. I think we need to get Apple support to convey to whoever can fix these recurring issues that users need to know when incoming and/or outgoing email is being blocked and we need the means to correct or challenge any blocking that is being done in error. This is a basic issue of trust and reliability. Thanks again to Apple for fixing the Gmail delivery problem, though.