I have experienced this issue on a number of deals. Often the cultural elements of an acquisition is neglected or low prioritized due to time constraints or lack of resources with the need knowledge of handling cultural aspects in the integration and transformation process.
Perceiving strong cultural alignment is dangerous in particular in across-border deals. But expecting cultural alignment between organizations within the same geographical area or country can be a mistake. And it can be a vital reason for destroying deal value.
Investing time and resources in cultural management/change already in Sign-to-Close period should be a prerequisite in any deal involving people/resources. This to avoid misalignment and misunderstanding each other once you bring the two organizations together. This will secure speed and success of executing the integration and transformation