I've just taken a look at your Patriot PSD48G266681 memory on the Amazon web site and the picture shows what I consider to be an unusal feature (i.e. I've not seen it before). If you look closely at the lower edge of the DIMM, you'll see the length of the gold plated contacts is greater in the middle and shorter at either end. It looks like Patriot have chamfered (ground down) the left and right-hand ends of the DIMM, presumably to make it easier to plug into the motherboard. My guess is you need less pressure initially during fitting, when only the middle section of the DIMM meets the socket contacts. This probably helps to get the DIMM seated, before the final hard push to get the latches engaged.
If the outline of your memory is identical and the metal contacts in your motherboard's DIMM sockets are particularly low down, there's the vague chance you're not getting good contact on all the gold DIMM contacts. It's a wild hypothesis, but I did have a similar problem with an old plug-in VGA graphics card. In this instance the opposite was true. There was too much blank fibreglass below the bottom of the gold plated contacts, so the GPU wasn't recognised by the motherboard. I had to file 2mm of blank fibreglass off the bottom of the card, so it seated lower in the socket and made electrical contact with the motherboard. If you do have this specific problem, the only solution is new RAM with no chamfer. I'd advise against filing down the centre of your DIMMs.
If the outline of your memory is identical and the metal contacts in your motherboard's DIMM sockets are particularly low down, there's the vague chance you're not getting good contact on all the gold DIMM contacts. It's a wild hypothesis, but I did have a similar problem with an old plug-in VGA graphics card. In this instance the opposite was true. There was too much blank fibreglass below the bottom of the gold plated contacts, so the GPU wasn't recognised by the motherboard. I had to file 2mm of blank fibreglass off the bottom of the card, so it seated lower in the socket and made electrical contact with the motherboard. If you do have this specific problem, the only solution is new RAM with no chamfer. I'd advise against filing down the centre of your DIMMs.