Micro SD cards work great in native micro SD slots but I wouldn't use them anywhere else. One problem is the adapters are generally cheaply made and often don't reliably fit the contacts in the device to which they are mated; I suspect this is why they often don't work well in Canon cameras. And with extensive use, the contacts inside the adapter itself are likely to wear and become less reliable in making contact with the memory card itself.
But even if the adapter appears to work reliably in the camera, there is another very good reason not to use them where maximum card performance is needed (like recording extended bursts of photos or 4K video) because the native card performance is often reduced by the adapter even though it is a purely passive device. Data transfer is occurring in the high RF (radio frequency) range and layout and length of the extremely short connecting lines in the adapter can and do reduce the transfer rate given the very high frequency at which high speed memory operates. One of the more useful discoveries in the high end test and measurement world during the 1950s was that a very short matched transmission line provides a useful short delay in signal transfer which is wonderful when you are trying to view the actual triggering event on an oscilloscope but not so wonderful when you want maximum transfer rate with a memory card. So your cheap micro to regular SD adapter is cheapening the performance of your expensive micro memory card.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
