This makes absolutely no sense.
First of all there shouldn't be any difference whether sRGB or Adobe RGB in color managed applications (aside from the occasional gamut clipping). So something is messed up here.
Second - that is a wide gamut monitor. Everything that is not color managed, and has sRGB numbers, will appear incorrectly oversaturated. Nothing should be desaturated on that monitor (except untagged Prophoto). If the file has Adobe RGB numbers it should look more or less normal.
I'm not jumping to conclusions without seeing screenshots, but the only explanation that comes into my head is that what you call desaturated is in fact the correct version. That in turn means a broken monitor profile so that Lightroom doesn't render correctly on-screen - in turn leading you to make bogus adjustments.
(If this was Photoshop, another explanation could be assigning sRGB instead of converting. Long shot, but if the Lightroom Export function was messed up, perhaps something like that could happen. If so, resetting Lr preferences might take care of it).
Basic troubleshooting 101: Set Adobe RGB as default monitor profile in Windows, reboot, and try again.