Would love to see a screencap.
I've seen "jaggies" before, but only on SD material - like DS9, VOY, and any given sitcom, daytime soap opera, game show, etc, that was videotaped or transferred/edited on videotape. Especially depending on how they're encoded for broadcast, one oopsie in converting that to MPEG2 and you'd have shiny new anomalies, but I digress.
Those wouldn't be vertical scanlines as such, but could yield an effect that could be perceived as such? (I've seen "AI" add more defined lines after removing moire to cartoons for virtual HD but live action is definitely a vastly more complicated situation, for which there are improvements but I'd still use it only if no other options exist; not to mention all physical media needs to be refreshed as films will decompose after x amount of years and decades, especially if the conditions are less than ideal (too humid or too dry, too warm, too cold, etc.) Never mind the quality of the film stock; some shows and music lose fidelity because of a bad film or tape batch too... digital data can go on indefinitely, assuming comparatively basic safeguards are put in place.)
Maybe Paramount Plus ( PP? P+? ) put up the wrong masters by accident, or in their streaming service is channeling them through an SD filter - if they separate SD and HD content into separate channels to rent/subscribe to.
It's probably one of those possibilities but there could be others.
