Deb, I also feel certain that you had a HOWR attack. The same thing happened to me on the first five eggs in 2014. I was new to blue-birding, and needless to say I was devastated. The experienced folks here on the forum told me about the wren guards, so I promptly built one and got it up for the second nesting (I removed the original nest and saved it in a paper bag). Mine is made from cedar like the boxes, and obscures the hole from the front and the sides. It is attached to the roof with a small hinge and easily flips up out of the way for box checks. I have used these on three successful hatches, and the birds usually accept them within 15 or 20 minutes.
Good luck on a second nesting.
BZ