Where do people get this information? No such thing. You will be fine with commuting, but CBP officers are not always well informed and sometimes they will send you to secondary inspection.
Of course every time you enter the US using H4 Visa, the H1B spouse must be already in the US or traveling with you.
The purpose of H4 visa is to join the H1 holder living in US. If the H1 holder doesn’t live in US, H4 visa is moot.
I too was under the impression that having valid H4 visa would be sufficient to commute with H1, but CBP very well know what they are doing in denying H4 commuters. This is not grey area for sure because nobody is successful in commuting daily on H4 visa at different port of entries .
The experience of members on H4 commute is consistent. In addition to this member ybx, another member, I think, rakatatoon also ran in to similar issues. His spouse was denied entry and was asked to get B2 for such travels despite showing a print out of appropriate laws created by attorney. Justinline also quoted a story where H4 holder was denied entry when she attempted to pick up the spouse from US side