When buying parts for cars in Upgrades & Tuning and attempt to save them, I get a message saying save failed, try again in 25 seconds. And I did that, but the issue still persists.
Are you able to save your car upgrades even with the error?
Could you try working through the network troubleshooting from these articles to see if that helps your issue. Network issues can affect game saves and other gameplay features.
Multiplayer, Online, and Network Connection Troubleshooting – Forza Support (forzamotorsport.net)
IPsec error message – Forza Support (forzamotorsport.net)
I was still able to save car upgrades, but not Designs & Paints. I do experience technical difficulties at times. The issue has now been solved. Thank you.