Surely if that's happening regularly then it's up to the manager to sit down individually with such employees and make it clear that it's no more acceptable to

Surely if that's happening regularly then it's up to the manager to sit down individually with such employees and make it clear that it's no more acceptable to be regularly unavailable during the work day when remote than it is when at the office. FWIW, it's not a problem I ever noticed particularly. There are always occasions when the exact person you might need help from or to collaborate with at some particular moment isn't available, and undoubtedly some things are better done working together in person, but I've never experienced the situation of "damn-near impossible to work with" with any work colleague, even during extended periods of working remotely (which I've been doing on & off since about 2005, sometimes in entirely different time zones to my coworkers!).