I am not sure what your post has to do with NMM wiping out all of my mods from the pligin.txt file, but your point is well taken.
On another note, NMM just upgraded itself, and the new 1.8 version has the same problem (it also blanks the plugin.txt file).
If you are referring to my post/advice, I was pointing it out because of your extensive mod list and because the problem you are posting is not seen by many NMM users, including myself. Therefore, it is not NMM per se that is clearing the plugins.txt file. If it was, it would be doing it for everyone. The problem has to be caused by something else or by some type of unusual interaction between NMM and something else (or even between two or more other things, but not NMM).
By the way, I have no idea what config setting you are referring to when you mention "bsomethingmods=1" in SkyrimPrefs. My SkyrimPrefs does not have that variable and I have used NMM since launch with no problems. With my current restart since last week, I have used both NMM and Wrye Smash/Bash, including launching with Wrye, but this is the first game I have launched Skyrim via Wrye and all my other games launched through NMM. I used up to NMM 17.1 last week, but haven't yet updated to the new 18.3 because I am using Wrye to launch right now.
Anyway... I suggest that you deactivate all mods, launch through NMM like normal (including SKSE, of course). Activate one mod at a time and test again until you find out what the problem mod is. That's really the only way to find the problem.
Oh, I also noticed something in your process description about the steps you take. There are two tabs in NMM: Plugins and Mods. Mods simply lists the mods you have downloaded and that are available for activation. Mods tab does NOT list the mods that are actually active for your game. That's what the Plugins tab is for.
In the Mods tab, you select the mod you want to activate and activate it. You can click it an install it using the button on the left sidebar menu, or you can simply double-click the mod you want to activate. Either method works. Once you do that, NMM installs the mod as a plugin and automatically activates it in the Plugins tab.
You can review your active mods/plugins in the Plugins tab. You can also change the load order manually there or deactivate specific mods without uninstalling them.