The short answer is, you've hit a threshold referred to by IBM as a "pivot year."  

Remember Y2K? Well, a pivot year was a technique developed to handle dates with a 2-digit year, where the century wasn't known. The system considered any year 39 and under to be 20xx and any year 40 and over to be 19xx. While many programs and files that used this technique have been adjusted over the years, there are still many places where the database stores only a 2-digit year, so the pivot year logic is used.

A certificate opened in 2022 with an 18-year term puts the maturity date into 2040. The solution, of course, is to use 8-digit dates everywhere, and then dates in 2040 and beyond can be treated just like any other date. That sounds simple until you realize that every single date in every single program and every single file, from CD creation to maturity, must be adjusted to an 8-digit date. This includes all screens, forms, CD creation, CD maturity, rollovers, closing programs, programs related to HSA and IRA CDs, and likely others.  

During the File Expansion Project (FEP) in 2014, we updated dates in major files like the MEMBERx account information files, but that project did not update every single work field in every single program, since we had to draw the line somewhere to get the project done. This issue is an example of a work field that did not happen to get updated during that project. CU*BASE wasn't really designed with certificates of this length in mind. The CD creation program is using a 6-digit date work field when calculating the maturity date of the CD. Fixing that one program is fairly simple. Walking a new CD through the entire process to test all the possible branches of a CD’s life, however, is going to be a time-consuming effort. The amount of time that will take depends on how many other programs need to be changed and tested. 

We do have a project to address this on our long-term planning radar. However, with current resources it will likely be at least a year or two before that work can be completed. In the meantime, you will need to adjust the term of your long-term certificates so that they do not fall into 2040 or beyond. After all adjustments are made and tested, you will be able to adjust the maturity date on those individual accounts accordingly.