You won’t get far through a conversation about subgrid in CSS Grid Layout without someone suggesting that display: contents solves most of the problems anyway, so do we really need subgrid? This really isn’t the case, display: contents does indeed solve a class of problems, but these are different problems to those that subgrid would help us with.
Rachel Andrew explains in detail how
display: subgrid is different to
display: contents. Interestingly, I had a similar issue just the other day. In my situation however,
display: contents would’ve worked perfectly. If you’re trying to keep up to date with all the new layout stuff, this article is a must-read.