OK. If the picture shows the chain tension when the bike is in lowest gear (small chainring/biggest cog), then IMO the chain is most likely too short. I'm sticking with that...

The whole rule of measuring chain length according to BIG/big + one link is only a rule of thumb. It works OK with typical gearing modern road bikes, but it can be downright wrong. An alternate method of determing length is to put the bike in highest gear, and set chain length so that the jockey wheel is vertical. In this case you may be better off making it as long as possible. Put it in SMALL/small (5th), and make the chain as long as you can. Should be just short enough that the jockey wheel doesn't hit itself. There is often a range of chain lengths that technically are OK, but often one particular length will shift best and feel smoothest.

Besides double checking in your limit screws, also check for stiff links. I don't think that's the issue here, but it should always be checked.