I was playing a game as Tahm Kench and I'm not sure if its a bug or not but I ate my Kindred when Morg ulted thinking that would defend her from it but next thing I know she died inside of me, and to my knowledge only dmg overtime can do that, now I always thought Morg's ult worked a bit like Zed's Ult where it just took some time in activating so am I wrong, or was it a bug?
Deep Terror Nami7 votesTethers only break from being cleansed or leaving their range, and are considered a type of DoT due to this.
Vesarixx2 votesIt's not really a DoT, there is an initial damage portion when it is first cast and then a secondary damage portion when the stun occurs, similar to Leblancs chains
Vesarixx3 votesOk, I'm not sure why you posted that, 
s tormented soil is the only ability of hers listed as a DoT effect on that page.
Active: After a 0.5-second delay Morgana latches chains of energy onto nearby enemy champions, dealing initial magic damage. The tethers grant True Sight icon true sight of affected enemies and Slow icon slow them by 20%.
Targets who did not leave the tether range after 3 seconds are Stun icon stunned for 1.5 seconds and dealt the same magic damage again.
There is not Damage over Time effect as part of this, there is a persistent slow, but the damage is instant application.
Deep Terror Nami1 votesThere's a section for tethers...
Vesarixx2 votesThat's for tethers that have a DoT component, Fiddle Drain applies constant damage every second while the tether holds, Soul shackles applies 2 instances of damage, not constant damage. Not all tethers are DoT effects, Leblancs E is also not listed on that page for this reason.
ForgottenLuck1 votesAhhh ok did not know that thank you for the answer
dannykun1 votesMorgs ult is a tether, so if the person who is tethered doesn't leave the range of it they continue to be under the effects of it. The same goes for all tethers, of which the only one coming to mind is fiddles drain, the same concept applies in all these cases though.
Vesarixx1 votesThe tether effect of her ult is not broken by untargetable abilities unless the leave the range of the spell, you can see the same effect as Vlad when Fiddle is casting drain on him and he pools.
Sneakyy XD1 votesZed's ult will also deal damage to champion consumed by Tahm.
ForgottenLuck1 votesNot really unless I got a bug because I have saved many allies from zed with TK
EvilMerodach1 votes ulti is done in 2 instances, once at the start, which makes a line connecting all champs in range to her.
Ways to avoid the 2nd instance- move out of range, become invulnerable (kayle ulti/hourglass), cleanse/qss/spellsheield (noc, sivir), or kill her before the 2nd instance goes off.
Tahm eating an ally doesn't make them invulnerable, just "untargetable" (like fizz/vlad).
So for tahm to save the ally, they would have to eat them, then walk/flash away from morg.
CoolKnightST1 votesIt's a Tether so it will aply even when the target is untargetable. It's similar to karma's W. With hourglass you get the same effect too. It's not really an dot since tether damage aply on activation & one time on the end of the duration. An dot deals damage every x seconds until the end of the duration.
LegendaryLemur1 votesI believe that Tahm's devour applies Stasis, same as Zhonya's hourglass, rendering the target invulnerable (all damage reduced to zero) and untargetable (can't be the target of new abilities).
Neither invulnerable nor untargetable removes tethers or DoTs (invlunerable prevents damage from DoTs while it lasts, but if invulnerablitiy expires while the DoT is present you will begin/resume receiving damage) nor does either invuln./untarg. prevent CC.
Untargetable does not remove tethers nor does it prevent CC.
My understanding (have not tested) would be that if tahm devours someone tethered by soul shackles, it would not break the tether. If devour ends before soul shackles then both the stun and damage would apply. If soul shackles duration finishes first, then the stun would still apply but the damage would be negated by invulnerability.
So Soul Shackles is unaffected by devour (apart from preventing the tether from ever forming in the first place on an already-devoured target).