Thank you Lillian on your comments and suggestions. Now that I think of it, you are absolutely right about the developer amount. I only used 2L of developer in 16x20 tray and it might have oxidized and cooled too rapidly for consistent results. I'll be using more developer next time. Great catch!
This was my second attempt at making lith prints and this time everything was going wrong from popping negatives to spots on paper and oxidized developer. Truly, lith printing is one of the most difficult techniques to get right!
By the way, I wanted to mention that I loved the way you packed the prints you sent to me, so I shamelessly stole the idea and used it for sending my prints. Thank you!