The bug
In the game there are so called "random ticks" that make crops grow, copper oxidize, cauldrons to fill up, amethyst shards to grow, etc. However, there is a bug in the game that discards half of the random ticks in the world, thus resulting in slower growth of crops, making copper oxidize slower, and cauldrons taking longer to fill up. Code digging confirming this issue has been published here: https://twitter.com/fragmites/status/1450965142045278214?s=20

If this issue is fixed, it may also fix other issues that involve random ticks, some of which are described in the reports linked as “relates to” below.

Steps to reproduce
Step 1: Make this setup of dripstone and 10 cauldrons:
or use the provided world download: Lava cauldron test.mcworld
Step 2: Wait 13 minutes
(Note: Randomtickspeed must be set to the default:
Bedrock: 1
Java: 3)
Step 3: Count how many cauldrons are completely filled
Step 4: Repeat it multiple times and also compare this to Java Edition as well

Expected result
About 50% of all the cauldrons are filled, like how it is proposed in Java

Observed result
About 20% of all the cauldrons are filled

Notes
Even though Bedrock has randomtickspeed 1 compared to that of Java with randomtickspeed 3. Bedrock should randomly tick 2.5 blocks per gametick and 3 blocks on Java edition, however on Bedrock edition they tick 1.25 blocks per gametick because of a bug. See the code analysis by Rufus provided by the Twitter link as well as the comment below this bugreport: https://bugs.mojang.com/browse/MCPE-145612?focusedCommentId=1094552&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1094552