This assertion is not passing on all the supported platforms/compilers (notably x86 macOS). The exact assertion is actually not that important though, especially on the 6.0 branch. The assertion is meant to help mitigate the risk that a data member is added which we forget to account for the size of in our memory budgeting. This risk seems very low on the 6.0 branch, so I propose we delete the assertion on 6.0 and leave it on master branches to keep that protection, which should prevent anything from being backported to break 6.0.