In light of the recent upgrade of the Kusama relay chain, an XCM issue has surfaced. This problem arises because the Kusama relay chain appends a SetTopic instruction to every XCM program. However, XCM version 2, which is currently the default for many destinations, does not support this instruction. Consequently, when the Kusama relay chain sends an XCM message to a destination, it believes is using v2 (even if that destination has actually upgraded to v3), the SetTopic instruction triggers an error, leading to failed transactions.
The mismatch in XCM versions can lead to issues between the relay chain and parachains. To resolve this, we propose setting the relay chain's safeXcmVersion to v3. This adjustment ensures that the relay chain will send XCMs in the v3 format by default. Moreover, defaulting to v3 on the relay chain isn't just a temporary fix. It's a strategic move for the long term.