The bug
In 1.13-pre4 crops were uprooting properly during a block update at block light level 7 and below. Now in 1.13-pre5 block updates do not uproot crops that have a lower than required block light level.
Further testing shows that crops cannot be planted in light level 7 or lower (this is new) but planted crops in light level 7 from a previous snapshot, when loaded in, do not grow but also do not uproot.
Linked issues
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This is no longer happening in newer versions of the game as per MC-257741 (which got erroneously resolved as a duplicate of this bug report, adding 1.19.2 to affected versions) and recent testing by @unknown for MCPE-36863. Resolving as Cannot Reproduce.
This effects version 1.14.1 Pre-Release 1. Crops no longer pop off the farmland when light level is reduced below the threshold. (See attachments "2019-05-08_10.03.00.png", "2019-05-08_10.03.05.png" and "2019-05-08_10.13.37.png")