Well, I just realized today that the ground plane of my board extends under the antenna of both the ESP-01 & ESP-03 that my board is targeting.

As someone with RF experience will tell you (which includes myself, believe it or not considering this dumb mistake), a ground plane will reflect the RF energy from the antenna (see the Wikipedia article on ground planes). Which is great if you're trying to receive the signal. If you're trying to transmit the signal, it won't be able to go through the ground plane, which can wreak havoc when you don't know where your receiving WiFi antenna is.

So, I'm currently in the process of redesigning the board to counter this problem. Since I needed to make this change, I decided to fix some of my other qualms I had about the board (such as spacing of pin headers, layout, grouping switches, etc), and make the layout more uniform. I'm also planning on adding mounting holes, since I'm looking at expanding the size of the board to accommodate the full length of the ESP-01 board (on the previous version, it would overhang the edge of the board, which could possibly leave it unprotected depending on the situation.

I'm also adding labels to make the operation of the board more transparent.