Something's wonky because I tried with 5.26.1 and 5.32.1 (which is what I had installed handy) and both griped with the (expected, due to strict) bareword not allowed. Longshot (and this is really straw-grasping) but you might check your PERL5OPT environment variable and maybe see if you've got something that might be pulling something in and defined CP_UTF8 wherever your 5.28 is (presuming this is on different machines with different environments; if it's the same box / same user / same environment . . . it is a puzzlement).

Addendum: Not that you've not already worked out the solution, but if you're trying to track down what's happening . . .