Important: There was a slight hiccup with the tagging of 3.3.4 - the split packages TYPO3.Flow, TYPO3.Fluid, TYPO3.Eel and TYPO3.Kickstart, neos/utility-objecthandling have been re-tagged, so you should update.
The tags were done wrong and then a re-release was triggered immediately, the development collection at https://github.com/neos/flow-development-collection/ had the correct tag. But the split repositories (at https://github.com/neos/flow/, https://github.com/neos/fluid/, https://github.com/neos/eel/, https://github.com/neos/kickstart/, neos/utility-objecthandling) were not re-tagged accordingly.
This had next relatively little influence, but a breaking change found it’s way into Flow (leading to the history module in Neos not working).
This morning we re-tagged 3.3.4 in the affected repositories, so you should run composer update to get the correct code. Or you do that later today, when a fresh patch level is expected to be released…