It is expected if no reasonable fee is likely to get your transaction into the next block, which is currently the case as there seems to be unusually high transaction volume.
How could it calculate fee for two blocks and not give a fee estimate for one block ? Also I don't see any spike in tx volume , its been same as last few days ...
I am not sure how the estimatefee algorithm works but I would assume it would track transaction in mempool to see how many blocks it took them to confirm and then take an average of fee/byte for each number of block.
