Yes, any lye solution normally used for soap making will absorb water from the open air, just like solid alkali (NaOH or KOH) does. Keep the container of masterbatched lye solution tightly sealed as much as possible to minimize this problem.
I also store my jug of masterbatched lye and all containers of dry alkali in a low humidity "dry bucket," but if you have a sturdy lye jug and keep it well sealed, that works well.
Lye solution weighed into an open container and left to sit for awhile will also absorb some water before it's used in soap. This extra water is absorbed after the solution is weighed, however, so it will not mess up the weighing process.
You can evaluate the amount of water absorbed by weighing the container of lye solution right after the solution is weighed and a second time right before you use it. Did the weight change? If so, the increase is the water absorbed.
Another issue to keep in mind is NaOH or KOH also reacts with carbon dioxide in air to make sodium carbonate (washing soda). If you're getting a lot of white "lye lint" on top of your lye solution, that's evidence of this happening.
Sodium carbonate is less effective alkali for making soap, so this is a second reason to keep your lye solution protected from the open air.
If you get "lint", it's not necessary to strain it out before using the lye. The only reason I strain lye is if I use an opaque or dark liquid to make my lye solution and I can't be 100% certain I've got all the NaOH completely dissolved. Then I strain so I know.
