Good question! 👍

Yes there is, I'll try to explain:

Let's say You do coinjoin now 5 times in a row. With each coinjoin there are in total 20 different participants, so per coinjoin You'll get an anonymity set of 20. After 5 times, You now have an anonymity set of 100. So far so good. But after a week, another participant of one of those coinjoins You've participated in, decides that he wants to sell his sats on a kyc exchange. By doing that, his sats are de-anonymised. But it has implications for your anonymity set too, because one of the coinjoin outputs got 'doxed', so effectively your anonymity set became 99 now. As You can imagine, over time more of those coinjoin participants do stuff with their coinjoined sats and are 'doxing' their sats, so your anonymity set decreases because of that over time, eventhough You didn't do anything with your coinjoined sats.

If You'd do again a coinjoin after 1 year and there are again 20 participants in that coinjoin, You are sure that You've got at least an anonymity set of 20 again per coinjoin at that moment again.

So as You might understand, getting privacy by coinjoining is one thing, but keeping privacy is another thing.

Also, if You get multiple outputs from a coinjoin, for instance 2 utxo's of 0.05 btc, never move them after a coinjoin to the same adress. Because by doing that, You'd show chain analyses companies that those 2 piles of sats belong to the same person which off course already decreases your anonymity set of your sats.

Let me know if this explainating made sense to You. 😃