Triage: Both scenarios are reproducible, but probably working as intended (mostly).
For the Mr. Mime situation:
- If you were playing at a table in the year 2000, poison does not disable invisible wall. The card text does not list it.
- If you are playing with a base-rocket card pool, but applying all compendium rulings that eventually apply to the card, then poison does disable invisible wall even though it doesn’t list it on the card.
I think the TCGOne policy leans towards the latter understanding based on what is in this other thread: WotC Erratas, Complete List - #10 by JasonKlaczynski
For Venomoth, the in-play check for shift only applies at the time the shift happens and is not cleared between bench/active (compendium rulings).
Quirk: when Venomoth changes to Lightning, it becomes a Lightning Pokémon in play. The card actually says “other Pokémon” though, so probably shouldn’t have its own type as an option. Through testing, it can be observed as an option to go L->L, so this effective no-op might actually be a bug.
Disclaimer: I’m not a judge or expert. This is from repro testing and rulings investigation.
This was interesting. Makes me wonder if it could be possible to surface all the compendium rulings that apply to a card in-game. 
(this would not be an easy thing to do)
Citations:
Mr. Mime / Invisible Wall:
- Jan 17, 2002 Special Conditions change — “They ALSO shut off ALL Pokemon Powers”
- The disclaimer extension — every A/C/P clause “should ALSO include Poisoned”
- Invisible Wall’s 30-inclusive threshold (May 11, 2000 Q85)
- Wall blocks attack damage only, not Damage Swap etc. (Jun 29, 2000 Q389)
- Scope of the change (Jan 31, 2002 Q153): powers without an A/C/P disclaimer are NOT shut off by Poison — Invisible Wall has one, so it is
Venomoth / Shift: