I can confirm this, whenever I wake up around 4 am and randomly decide to go on some missions, the game says that the servers are unstable around that time. Luckily, it doesn't prevent us from being able to play, it's just a warning.
On topic question, around how much unit/squad total power is needed to clear the final level in each of the phases? I find myself wiping on the first mob, which is a huge difference from the third levels (?-3 and ?-7) which are very very easy to complete. Here's my current team:
At what point do I attempt the Ultimate maps?
Note: I could clear the Edelweiss Ultimate maps with a much weaker team than this, which is why these Ultimate maps got me confused at their difficulty. I just want to know at around how much power do I start spending Stamina attempting the Ultimate maps.