Hello,
in the V3 beta topic, the user Ajackpot talked about castling issues in Chess.
I can confirm that in the latest update indeed some problems related to castling have been introduced.
For example:

1. Pe2-e4. Nb8-c6
2. Pd2-d4. Pd7-d5
3. Pe4-e5. Bc8-f5
4. Pc2-c3. Pe7-e6
5. Nb1-d2. Ng8-e7
6. Nd2-b3. Pa7-a6
7. Ph2-h4. Ra8-a7
8. Pg2-g4. Bf5-e4
9. Pf2-f3. Be4-f5
10. Ph4-h5. Ph7-h6
11. Pg4xf5. Ne7xf5
12. Bf1-d3. Pa6-a5
13. Bd3xf5. Pe6xf5
14. Pa2-a4. Nc6-e7
15. Ng1-e2. Qd8-c8
16. Ne2-f4. Pb7-b6
17. Qd1-e2. Pc7-c6
18. Pe5-e6. Ra7-a8
19. Pe6xf7+. Ke8xf7
20. Rh1-g1. Ra8-a7
21. Bc1-d2. Ra7-c7

Here, I don't understand why the Playroom doesn't allow white to make a long castle and considers the move to be illegal.

Thanks.

Hello,

It should be fixed now with the update of this morning.
Thank you for reporting.