The previous episode ended with a character talking loudly among walkers (which would attract their attention, of course). This episode then skips that point in time, picks up a few minutes later with the talking having no consequences. Later, although the character isn't as loud as before, talking draws walkers quickly.
Daryl igniting the pond would not only have contaminated the water supply, but would have lit the night sky, easily seen by walkers and the living for miles.
Right after Daryl blows up the biker gang with the RPG a motorcycle is seen still upright. There's no way a blast like that would have left a bike standing.
Due to the positions of the bikers spread across the road and their distance from the truck, several would have seen under it all the way to its back, and to its side (under the open door). They would have partially seen what was happening with Daryl.
Right when Abraham and Sasha start shooting from assault rifles, they are actually holding the guns with opposite hands. In the next frame Abraham starts to talk and holding the gun with the correct hand on the trigger.
The video must be horizontally switched.
When Abraham and Sasha are talking to the bikers, you can see a car coming up the road behind the bikers just before they are blown up by Daryl.
At minute 21 right before Ron points the gun at Rick someone can be heard saying "turn around"
There is no reason for Maggie to need help at the top of wall. Once Enid reaches her, it is clear that Maggie simply could have stepped on to the platform built into the wall that Enid is on.
As walkers were closing in on him, Glenn could have just climbed the wall (like Carl kept doing) to escape them.
When Abraham and Sasha save Glenn in Alexandria you can see, that Abraham is holding an assault rifle with his right hand. However, a second later, he is suddenly holding it in his left one instead.
The group did nothing to prevent the other half of the walker horde (that didn't go to Alexandria) from returning. Since they are distracted by almost anything (and may migrate), there is nothing to stop the horde from reversing their course and heading right back toward Alexandria.