In fact it must be not so rare as I have the same daughterboard rev7 in my original A3000-16Mhz.
Never has failed, the machine was overclocked to 25Mhz, upgraded with a A3640 and has been fully populated, both onboard RAM and Zorro boards (right now, an Opalvision, a genlock and an AT-BUS 2008 boards). The AT-BUS has been maxed out and this way I've get rid of an old A2058 board.
So, do you have these problems only when x-surf and Bigram are placed togheter?