Lab: Digestion of albumin with pepsin, source of error?

Hello! So I did a lab on the digestion of albumin with pepsin to find out the reaction rate for pepsin (under different circumstances) by measuring the absorbance a couple of minutes after adding albumin to test tubes containing pepsin and other different things. In one of the test tubes there was no pepsin, only water (distilled) and albumin. This tube showed the lowest absorbance, which really confuses me since it should have showed the highest absorbance. What could be the source of error in this? This was the last tube to have it's absorbance mesuared, but that shouldn't matter since there was no pepsin in it.

Also is there any other stuff, good to know about this lab?

(This is my first post, I hope I did everything correctly!)