The changes between 1.14 and 1.13 are not quite compatible, and as such the pack_version should have been changed to 5:

• Resource packs made for the 1.14 that change particles or paintings don't have the same effect in 1.13.
• Resource packs made for the 1.13 that change stone slabs don't have the same effect in the 1.14 because the texture was renamed to smooth stone and the old file name is not recognized.