Submitted by KingNFT, also found by zhuXKET and 0xDING99YA.
The _matcho() function is not implemented properly. It might revert while the taking amount is greater than the best offers amount, which leads to order a matching failure.
The following test script shows how to trigger the issue:
And the log details:
Lets take a look at this line, we find the actual take_amt is 0.9999e18 RUBI, rather than the expected 1e18; the difference is exact the 0.01% of fee.
Back to the source code, we can see the issue arises on L1313 of _matcho(),  where m_pay_amt should be something like m_pay_amt + fee.
See PoC
daoio (Rubicon) confirmed via duplicate issue #1336
