This is directly related to the MAX. It is a snow ball effect. For example I have an E-175 shifted to as CRJ. The e-175 is taking over for a 319.
319 is replacing a 738 and the 738 is replacing a MAX. This happened this week as the schedule adjustments were made system wide. Cancellations allow aircraft shifts and the PDX-IAD is an example. Goes back to original schedule on Aug 1 for my above example along with over 300 others. My example starts with a IAD-GSP shift.