Two traits:

var ic2_access_01 = mods.compatskills.GameStageUnlockable.addGameStageUnlockable("ic2_unlock", "ic2_unlock", 2, 0, "compatskills:engineer", 1, "not|trait|compatskills:botania_unlock");

var botania_access_01 = mods.compatskills.GameStageUnlockable.addGameStageUnlockable("botania_unlock", "botania_unlock", 0, 0, "reskillable:magic", 1, "not|trait|compatskills:ic2_unlock");

The one created first does not actually take the "not|trait|compatskills:XXXXXXX_unlock". The second trait will take "not|trait|compatskills:XXXXXXX_unlock". I believe it is due to the order they are created in because if you swap them the requirement only stays with the second trait created.

The reskillable.cfg does show the traits correctly...even deleted the file and let it remake but only one trait shows the actual requirement in game depending on which is made second in the script.

"compatskills:botania_unlock" {
B:Enabled=true
S:Requirements <
not|trait|compatskills:ic2_unlock
>
I:"Skill Point Cost"=1
I:"X-Pos [0-4]:"=0
I:"Y-Pos [0-3]:"=0
}

"compatskills:ic2_unlock" {
B:Enabled=true
S:Requirements <
not|trait|compatskills:botania_unlock
>
I:"Skill Point Cost"=1
I:"X-Pos [0-4]:"=2
I:"Y-Pos [0-3]:"=0
}

Will attach a screen shot of each trait in the gui.

and

I am leaving this open, as there is still the issue when it is done purely through the reskillable config with reskillable traits, but it is technically now possible (as of 1.14.1) to do using the bracket handlers to override it afterwards. (It may still throw a warning/error in the console saying it doesn't exist but it should properly work).

<unlockable:compatskills:botania_unlock>.setRequirements("not|trait|compatskills:ic2_unlock");

Sometime after the call creating the ic2_unlock skill is made.