Some users who have updated their Macs to OS X 10.10.3 are noticing certain specific drops in Wi-Fi connectivity, although they are not those problems that they experienced when Yosemite was launched on the market and that lasted until the latest versions of the system.
In any case, this time there is no need to be alarmed because it seems that the error is localized and can be solved in a simple and fast way without having to search through multiple different options to solve it. Specifically this time it is an incident in the synchronization between iCloud and the Photos application.
The new Photos app replaced the iPhoto app on your Mac when updating OS X 10.10.3 overwriting part of the information of it since it is a replacement, replacing the experience with one closer to iOS. Depending on the system it is possible that this failure only occurs in certain computers and does not affect all equally, without going any further in any of my computers it has happened to me when updating.
This new application like the iOS version, not only manages the photo library locally but also has the option to sync with iCloud and this seems to be the cause of some Wi-Fi connections may not work.
For now there is no satisfactory or definitive solution until Apple releases a patch that solves the problem, but we can proceed to disable certain iCloud-related settings so that the problem does not reproduce, especially if you tend to use your local photo library more and only use iCloud as a synchronization service for documents or games. The steps to follow would be the following:
Open Photos
Go to the Photos menu> Preferences.
Go to the iCloud section
Uncheck iCloud Photo Library
If after doing this the Wi-Fi connection becomes more stable, then we will leave it at that. If we see that the problem continues, then we will try to uncheck the other remaining options including My Photos in Stream and Photos shared with iCloud.