Would you be willing to file this issue with Chrome/libwebp? I'm not sure if your test case will reproduce the exact issue, but you quote the relevant bits from me in comment 8 to explain the issue. Feel free to cc me on that bug. https://bugs.chromium.org/p/webp/issues/list
Bug 1761275 Comment 12 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
Would you be willing to file this issue with Chrome/libwebp? I'm not sure if your test case will reproduce the exact issue, but you may quote the relevant bits from me in comment 8 to explain the issue. Feel free to cc me on that bug. https://bugs.chromium.org/p/webp/issues/list