I would be happy to add a fixpos per cycle cost or otherwise modify the behaviour of .fixpos, but that is a DCR (Design Change Request) not a bug. If there is not one already, posting a topic specifying the requested change in the Suggestions forum would allow me to track it and not forget about it. Thanks.
I started the thread in Newbie. At that point I didn't realize that an evolving zerobot might select to use .fixpos; I just wanted to know why my bots became stationary.
This issue has nothing to do with the waste threshold, although I may have inadvertently reported a bug regarding waste threshold. A higher waste threshold does not prevent bots from storing to .fixpos deliberately.
A .fixpos cost would be a nice fix until the rest comes down the pipeline, but I have to admit that this thread doesn't have much validity by the visible editorial stance on this forum. It's not really a bug that bots can select for .fixpos - it's just that there's no cost preventing them from doing so.