Steps to reproduce

1. Set randomtickspeed to 0.
2. Plant a bed of 500 kelp with several blocks of water above to allow room for growth
3. Start a stopwatch and set randomtickspeed to 1.
4. After 1 minute set randomtickspeed back to 0.
5. Count how many kelp growths you got.

Expected results

About 146 kelp growths. (Based on 1.16.0 changelog stating 100% chance of growth/tick: 500 plants * 1/4096 chance of each block being ticked on each tick * 1200 ticks/minute = 146.)

Actual results

A lot less than 146 kelp growths (less than half that number).

Kelp growth in automatic farms has slowed to a crawl. Unsure if this is intended.