After Y=137 block update start working wrongly making bud switches using a piston to detect a block update doesn't work as expected for example a block updated on Y= 138 cant update a bud switch with a piston on altitude 137,but after Y=200 it seems to happen every few blocks you can test it with any slime block engine built to increase Y
Please check if that's still an issue for you in the latest 1.14.4 stable release or the latest 1.15 (pre-)release.