We have found that the most common compatibility problems are due to the type of SD card being used. You are strongly advised to use an SD card from the recommended list on GoPro's website, http://gopro.com/help/articles/Block/microSD-Card-Considerations.
Use of cards not on the list, especially SanDisk Ultra cards, will greatly increase your chance of trouble with your setup. Some SD cards have the same product name as the cards on the list but are an older version that only has a U1 rating. Make sure your SD card has a U3 rating. Underperforming SD cards can prevent proper functioning of your GoPro camera's features.
For standard reliable operation, you need to use a U3 rated card which has a minimum of 30 MB/s read and write speed.
Just insert your SD card into your PC, select the drive and hit start.
Run the test a few times to make sure you are getting consistent results.
Make sure to either use an inbuilt SD card reader in your laptop OR use a good quality SD card reader plugged into a USB3.0 port. Use of a USB2.0 port will NOT give accurate results.
If you get a read/write speed of less than 30 MB/s, you will need a new card.
The SD card should be formatted as FAT32 or ExFAT.
The SD Association has two UHS Speed Classes, UHS Speed Class 1 and UHS Speed Class 3. UHS Speed Class 1 supports a minimum 10MB/s write speed, whereas UHS Speed Class 3 supports a minimum 30MB/s write speed. The UHS Speed Class is denoted by either a 1 or 3 inside of a U symbol.
As a rule of thumb, 4K-capable camcorders will usually require at least a UHS Speed Class 3 (U3) rated SD card.
Note that the "UHS Speed Class" is different from the "UHS Bus Speed". UHS Bus Speed is denoted by a roman numeral I, II, or III to indicate the theoretical maximum read and write speeds. However, unlike the UHS Speed Class, these are not sustained speeds. While the minimum speeds are very important for the device to properly operate, the maximum speeds should not affect the operation of the GoPro but may decrease the time needed to download the footage off the SD card.
You only need a "UHS Speed Class" of 3 (U3). Higher "UHS Bus Speed" cards can be expensive and not required.