Opening project in new Unity version - Slow?

This has been bugging me for a while. I updated Unity 2018.4.6 to Unity 2018.4.11. Opening a project with the newer version takes an awfully long time for Unity to make all the updates. It seems the that the slow down has something to do with the textures (Dialog box "Hold on.." followed by an image file). Anybody know what is happening? It seems that going form 2018.4.6 to 4.11 is a small increment, so what is it about the images is taking a long time?

 

Is this happening every time? Usually that's the kind of thing that can happen once (or occasionally) when migrating to a different Unity version. But usually it won't happen each time.

 

This is not first time this has happen, I'll have to monitor more closely when switching versions. I would just like to know what is it about the images that cause this.

 

Well, every time I update from one major version to Unity to another (for example 2019.1 to 2019.2), Unity seems to need to reimport everything. This is especially expensive for images, which tend to be pretty big. However, when updating to a minor/patch release (for example, 2019.1.13 to 2019.1.14), I wouldn't expect the reimport to happen, and it should be pretty quick. So, perhaps this happened after a major version update, in which case that's normal AFAIK. But if this happens all the time when reopening the project, then something's wrong.