I have cl_showpos on so you can take the coordinates in the top right and put them into Hammer.

These windows are visually open on Dam but there is clipping to prevent moving through them.

Leftover sprites. There are so many across the map I stopped taking pictures, it just needs a removal pass.

Wall doesn't meet the floor.

Support beam floats in the air.

Looks like a maligned texture because it's glowing red.

1) On final rounds for both teams, attackers have instant respawn and this to my understanding is a bug in normal Hydro. Attackers I think are meant to have the same respawn time.
2) There's a clip bush here in power plant spawn but no railing.
3) Leftover spotlights.

BLU base final point isn't team colored.

RED base vent might be misaligned because it glows red.

The crates nearby in RED base are a stuck spot without crouch jumping.

These doors could use a nobuild to prevent building inside them (may apply to every other door too).

You can stand over this cliff from Dam v Power Plant.

This cliff's texture looks odd by the game space and the dam pipe is floating.

This ladder by powerplant isn't functional.

Nor this one.

You can reduce the map's file size by omitting custom tool textures from your packing process. Nobody except you will likely see them anyway, so it's totally fine to be missing this texture.

No textures are replaced in the skybox.

Leftover wall.

Leftover dirt.

Dam v Radar Dish forgets to disable this barrier.

From normal Hydro, this support beam is invisible.

This support beam doesn't meet the floor.

In Dam's garage, leftover metal textures.

From Hydro, no stair clipping in Dam spawn room.

No stair clipping and leftover sprites.

Only the first step was replaced.

Ground doesn't match the rest of the scene.

Walls weren't replaced behind here in RED final.

Hole in the wall at RED final.

This rope leads to nothing (probably a generator in the original).

Radar dish stairs aren't replaced.

Dam door text is backwards. Also, without swapping the door model/brush with matching team signs, it may be slightly confusing for players when the doors lie in their text. Considering how territories are meant to be neutral, maybe these doors can be neutral too to simplify things.

One side isn't replaced on the staircase.

Stairs have no clipping.

Could improve this by disabling vphysics and adding a clip brush to these railings on Radar Dish.

Inside RED's final spawn room, the door text is backwards.