Thank you for reporting the artifacts you have encountered.
What you are observing is a typical consequence of block compression: BC7 is a lossy format, and in some cases the decompressed alpha value can differ by one least significant bit from the original. This is expected behavior and part of how the BC7 format and its encoders trade bit‑exactness in individual channels for overall RGBA quality. If your content relies on strict alpha semantics (such as fully opaque pixels being preserved exactly), there are several options to mitigate this, such as switching back to the ISPC compressor in the Player Settings (which performs better on the provided texture in this regard), using a different compression format, splitting the alpha channel into a separate texture, or adjusting shader logic to account for small alpha deviations.
Over time, the team will continue improving compression workflows, and as part of that we will look more closely at how fully opaque and fully transparent pixels are handled. For now, the behavior you are seeing is consistent with BC7’s design and current implementation, so we recommend applying one of the above workarounds when exact alpha behavior is required.