Invalid escape character in c_cpp_properties.json

VSCode is suddenly unhappy with c_cpp_properties.json. My platformio.ini file contains the build flag

-DTEMPLATE_PLACEHOLDER="\'\~\'"

which yields to the following in c_cpp_properties.json:

with the message "Invalid escape character in string. jsonc(261)"

Everything compiles just fine but I have to manually fix c_cpp_properties.json in order for Intellisense to work properly. I did not have this problem before but I'm not sure what caused it. Any help appreciated!