Reinstall CMSIS pack via Pack Installer. Ensure the pack version is ≤5.4.0 (newer packs may introduce API changes).
MDK 5.25 was a mature release. By version 5.25, Keil had ironed out many early bugs from the 5.0 series (introduced in 2013). Many engineering teams validated their production firmware on this version and are reluctant to risk new compiler optimizations or pack structure changes that came with 5.26+. mdk-arm version 5.25 download
After installation, you need to activate a license. Reinstall CMSIS pack via Pack Installer