I think the problem with Training mode and previous NTL game are somewhat similar. The game setup for Game speed shows various settings for speed with some being Turn-based and some being Real-time. As shown in the drop-down menu here:
So what has been the problem with previously existing NTL was that it didn't say right there whether it was a real-time thing or a turn-based thing. Because as you can see in the drop-down menu (where the non-functional option is still listed), there's no 2 different versions for RT and TB but just one line without saying which it is. So people assumed there is just one version. But it wasn't true and the only way to see it was to look at the top row and check the color on this:
If it was green - because you previously had selected real-time lobby (or had played real-time before) - then you might get into the wrong setting without noticing and I think that's what has caused trouble which ultimately lead to admins deciding to remove the option alltogether even though it probably would've been enough to make it TB only.
So with people who had played NTL before are now switching to Training mode, a similar problem occurs and it's even more subtle:
This doesn't even show any time setting, as it is training mode. However the colored green/brown arrow on top is still there which indicates that probably there's still a marker on the table somewhere for it to be TB or RT with the according behaviour like
* table-time-out after time of inactivity while the game on the table is in progress (I think a few hours for RT vs. 40 days for TB)
* table-setup-cancellation when the table doesn't fill soon enough before it starts (I think ~1hr for RT vs. 1-2 days or so for TB)
* blocking of starting other RT tables if it is running in RT
* maybe max number of TB tables is affected?
* getting different kinds of push-notifications, mails, end-of-game-notifications
Apparently people who wanted to play long-term NTL games who somehow get into a RT-training mode now seem to be stuck with some restrictions that are from these RT-table-side-effects. The swap from RT to TB cannot be done in place at the table when training mode is selected. Instead you need to go back to "play now", select Turn-based there and then re-create your table.
Or well... I think it is possible on the table if you change back to normal mode, then select any TB setting and then switch back to training mode. (I think this might be solved a bit better on the new game-page-interface as the button to change between RT/TB stays there. But well - that comes with other problems so I'll stick to my usual workflow for now.)