If you add a unique tag to an entity (a tag that has not been added to it before such as a random string of characters) and remove the tag from the previous tick every tick, the game will have progressively longer lag spikes and will eventually force the server to shutdown. This does not affect TPS generally.

To replicate, have this JavaScript run in the entry point file of the scripting API (an easy way to generate unique tags):

import {world, system} from '@minecraft/server';
system.runInterval(() => {
    const players = world.getDimension("overworld").getPlayers();
    if (players.length == 0) return;
    const player = players[0];
    for (const tag of player.getTags()) player.removeTag(tag);
    player.addTag(`tag_${Math.random()}`);
});

With this running, the lag spikes began around 10-15 minutes into the test. Watchdog alerts will signal the lag spikes.

Despite there only ever being one tag on the player at a time, the game appears to have a build-up of them until it just stops working altogether. From my testing, it seems combinations of multiple tags cause the same issue, even if there aren't thousands of unique tags, thousands of unique combinations cause similar lag spikes.