Bubbles on the lens are usually like foam inside the lens. If there are still a few bubbles and are on the sides, it's still okay, but if there are a lot, it can make the lens blurry.
6. Diaphragm blade jammed
The blade on the diaphragm is what opens and closes the lens opening. If this blade is stuck, then you will have difficulty adjusting the photo exposure.
Source: https://amirhomephotography.com
Source: 7. Oil splashes on lens optics
There are many things that cause oil to leak and get in contact with the lens optics. This can affect the results of the photo, but it depends on the amount of oil and how far the oil spreads. However, if the lens is splashed with oil, it must be serviced immediately for fear of it spreading everywhere.
8. Cracked / gupil optical elements
A cracked optical element may or may not have an effect on the photo, but if it is only on the side, it may not have an effect on the photo. Just like bubbles.