When previewing the production, the photo slides seem to lag and do not sync with the audio cues set for the background music
This may happen if you add raw files, such as Canon's .cr2 raw. These are not really image files, but are binary files that contain a lot of information. Raw files are typically around 50 to 100 MBs in size, depending on the sensor size type (full frame, medium format, crop sensor/APS-C, micro four-thirds, etc ) of the camera used and require additional processing to "develop" the data into actual image files, such as JPEG or PNG files.
Do not use raw files in VideoStudio. Instead, use the camera's recommended processing software to develop the raw files into image files. There are other software that can be used to develop and output image files from raw files, such as Corel AfterShot Pro .