I also noticed that after the last patch and wrote a response a few days ago.
(I have previously reduced the defences at that settlement to prolong battles and reduce the amount of friendly fire damage that missile turrets were doing.)
Settlement is connected to supply lines with ample resources available to repair items
Copied and pasted here:
I did a little test with one particular callout and a game save.
Help defend Taffington Boathouse with 3 different responses from me.
Show up and watch the settlers and turrets beat the invaders.
The settlement improvements sustain some missile damage which self repairs and I get to loot bodies with a successful defence notice.
Don't show up and one outcome is a successful defend the settlement notice but no bodies to loot and the settlement self repairs.
Don't show up and get a failure notice. The settlement self repairs, with again, no bodies to loot.