if there is say four-five hours gap, then next blocks should came faster, to make an average result equal to the computed average.
How often you will find blocks in the future doesn't depend on how often you found them in the past. This misbelief is called
gambler's fallacy.
Nothing for six hours on more computers at once, is not normal IMHO, especially if I have experienced this strange behaviour more times, and everytime on majority of my computers. (I run from three to five wallets.)
This is strange but not something improbable, probability is usually counter-intuitive.
You find blocks and that means that miner works correctly, it would be very strange for it to work incorrectly for some periods of time but correctly for the others.
You can search in the debug.log for the following messages "SpreadCoinMiner : generated block is stale" and "SpreadCoinMiner : ProcessBlock, block not accepted" (without quotes). Every such message will mean that mined block was not accepted. While the first one can happen the second one would indicate a bug.
(debug.log is located in C:\Users\\AppData\Roaming\SpreadCoin\ on Windows 7 and ~/.spreadcoin/ on Linux)