According to the available information, the problem is with the new Predictive Store Forwarding (PSF) feature used by Zen 3 processors. Its task is to increase performance by predicting the results of the Load instruction, ie as in the case of branch prediction The Load instruction speculatively executes the following instructions in advance, which it can simply discard if it does not hit. Mostly, however, they hit.
AMD has now discovered that the new bug is at the Specter v4 level and that applications that rely on safe operation in the sandbox are at risk. These are cases where the PSF does not hit, and this can happen, for example, when the addresses for Load or Store change during the execution of the program.
According to AMD, Predictive Store Forwarding is (so far) a theoretical risk, although it contributes to faster application running. However, the company has not yet found any code anywhere that would be able to use incorrectly speculatively executed instructions within the PSF, and itself indicates that the security risk is still low. Accordingly, AMD now recommends that you continue to use PSF, as users would not be deprived of some performance unnecessarily without this feature.