In the Caer Lem caves, there are lots of little pillars you need to jump between to move around, so falling can happen often. At one point I had my Rogue use bonus action Dash, increasing their speed to 12 squares, it fell prone after 3 squares and lost the rest of their turn, despite having 9 squares of movement left. I should have been able to stand up immediately, but all I could do was end turn.
Not being able to act after falling prone regardless of remaining movement is an annoying issue that this game shares with BG 3.
Standing up from Prone takes half your total movement. Jumping takes a foot of movement for each foot you clear. So if you moved three and jumped three, that leaves 6, half of your move, therefore it was correct.
-Glimpse
No, I had 12, moved 3, including the jump, fell prone (Incapacitated), and had 9 left. The only thing I could do was end my turn, despite having 9 movement left. Even if it only considers my base movement of 6 and ignores the extra movement from Bonus Action: Dash, I should still have been able to stand up with no movement remaining.
At the start of my next turn, I got up but had only 3 movement because of standing.