@Mzpalmtree , we were victims of this on our last trip. I'm not sure if I'm keeping all of your details straight in my head, but we had a CL split stay 12/20-12/27 (where we booked the CL FP+ for 12/21-12/26) and then another CL split stay 2/23-3/2 (booked CL FP+ for 2/24-2/26). We discovered on day 2 of our Feb/March trip that our regular (free) FP+ were unmodifiable, and when we called DSS/IT, we were told the same as you...that it was because of the 7 day limit and, unbeknownst to us, the DSS person who had booked our FP+ for us (both CL and paid ones) had "fixed" the problem by booking the free FP as CL ones. Sounds great in theory, but we frequently change things up on the fly and really hated not being able to modify them...and the fact that we were never told that this would be the case. Supposedly the problem had to do with our 90 day booking window opening before the December FP already being used.
And we had zero offsite stays involved. In nearly 25 years of going to WDW, we've had one offsite stay, in June of 2018...and I personally don't even count it as a "real trip" because we were there for my H's work and only popped in to the parks for a few hours for 3 nights.
@GADisneyDad14 , is it possible that multiple split stays and/or the CL FP+ are what is triggering this for both me and
@Mzpalmtree ? I think I've read that Disney doesn't actually recognize "split stays", so according to them I've now had 4 stays in the past 2 months, and CL FP+ as part of all 4 stays.
Hope this all makes sense...it is very confusing and for some reason tough for me to articulate, lol.