In the following particular instances, it is not a bug:
In Nightmare Mode, Huge Grenade does in fact deal weapon damage (rather than the spell damage it deals in Story and Hard Modes). This was an intentional change for Nightmare Mode, done to make the encounter more challenging.
As for Terminate, it has always been a weapon damage attack in any difficulty mode that it appears, and it would have never worked to Force Shroud it - any such luck to the contrary is a mere coincidence (though probably not uncommon).
In other instances while Force Shroud is active and you know that you are being hit by a tech or Force attack, the issue is most likely that players and NPCs always have at least a 5% chance to hit with any ability, regardless of how high your defense is to that type of ability. So while Force Shroud is active, there is always at least a 5% chance that you could be hit by any tech or Force attack.
I don't like this anymore than you do. I know it's extremely frustrating to be hit by an ability that, for all intents and purposes, should not have hit you. Unfortunately, fixing this issue is not as simple as it seems, but I'll take a deeper look to see if there is anything we can do about it.
Sorry, but this is just farcical.
Right now, thanks to the obscene spikiness of Shadow/Assassin, there are basically 2 reasons to even consider one as a tank for a progression raiding group: Force Shroud and stealth (for sapping targets, combat stealth + rezz in combat, etc.). Stealth is a mediocre justification for bringing a Shadow/Assassin, as Scoundrels/Operatives are very potent healers and can do all of the same things. So basically, that list gets cut down to Force Shroud.
Now you're telling us that the supposedly-virtually-100%-reliable CD which is currently the ONLY differentiating advantage of the class isn't actually 100% reliable, and there's a gamble each time it's used that basically nothing happens.
Oh, and thanks to the inclusion of Saber Reflect (which has its own limitations but, quite honestly, is FAR stronger overall than Force Shroud), the only times that Shadow/Assassin even have an advantage with their most differentiating ability is on AoE F/T attacks.
Oh, and thanks to changing what is by far the most noteworthy AoE F/T attack in the game to M/R in NiM, you've completely cut that advantage away.
By all accounts, you've completely written the class out of PVE.
Both DPS specs are near the back of the pack in terms of outright DPS potential, and are limited by being melees that have very little additional benefit to the group.
The tanking spec is the hardest to heal (even if it theoretically requires the least healing), it has the most mechanical disadvantages (heavy reliance on active mitigation mechanisms, situational-type CDs, and a frankly broken self-heal mechanic that cannot possibly scale in a balanced way), and now new content is being designed to bypass any advantages the class actually had.
Just go ahead and say it David... the development team just wants everyone to roll Juggernauts and Guardians and get it over with. The changes to all 3 tanking ACs in 2.0, the design of content in S&V, and now the design of content in both TFB and S&V NiM say that quite clearly.
VGs/PTs don't have the CDs to be as useful in the hands of a skilled player (anyone doing NiM content) as a Juggy/Guardian. They have no other differentiating advantages to bring to the table besides simplicity and smooth damage-taken profile. Only problem? Juggy/Guardian is now simple, with basically an equally smooth damage-taken profile, but also have fantastic CDs on top of that.
Shadows/Sins are spiky and are heavily dependent on hard-to-balance active mitigation mechanisms. They are the "skill" tanks by BioWare's own admission, but the ability to leverage the skillful elements of the class to gain commensurate benefits have been slammed into the ground by a combination of changes to core mechanics, content design, and rebalancing efforts in the other tanking ACs.
I hate to be crass, but this situation is straight-up ******** and it's completely unacceptable that BioWare sees no problem with it. You have rendered 2 out of 8 ACs basically moot in PVE endgame now, as neither Assassin/Shadow nor PT/VG are desirable as DPS classes, neither is on equal footing as tank classes, and now content is being designed in ways that further reduce any advantages they might have retained.
Outstanding individuals can certainly make any class *viable*, but those same outstanding individuals, if so able, would be congregating on a handful out of the available options (Sniper/Gunslinger + Trooper/Commando DPS, with the occasional Sentinel/Marauder for their raid buffs, Juggy/Guardian tanks, and some combination of a Sage/Sorc healer + any other healing AC). This is NOT okay.