How to recreate:

Create a contraption like in the image below ('setup example'). Have the two impulse command blocks activate the adjacent one, whilst the chain blocks deactivate their origin impulse block. Also create a clock adding a score to any dummy player, and display that score on a visible scoreboard (for visual representation of lag). Make sure to activate the clock.

Once the clock is activated, set the 'redstone needed' to 'active' in one of the impulse blocks (doesn't matter which one). After activation, watch the test dummy score go up, but rapidly slow down in the rate of increase, until it comes to a full stop. When the score increase freezes, the game will start lagging FPS-wise, and will eventually freeze as well. Consequences of this will be that when the player relogs, the chunk resets to an older state before the 'redstone needed' button was set to 'active'.

By activating / deactivating I dont mean powering the impulse block, but switching the "auto" tag. This causes buildup lag.

Current discoveries:

• Does not care about amount of RAM used (same outcome with 1/2/3GB
• /gamerule logAdminCommands does not decrease nor stop this bug from happening.
• Neither does /gamerule commandBlockOutput, nor /gamerule sendCommandFeedback

EDIT: Added crash report to attached files.
EDIT2: Rephrased title.