Slow down while looking back over sub.
 

Does anyone else experience this, as this has only just started happening to me after 2 weeks of playing.
While submerged when I look through the periscope astern back over the sub my frame rate plumets to single figures from about 80 fps .
In external view close up I get the same result. It is if there is an anomally that I can't see is causing a conflict of some kind.
How do I stop this as it is becoming very anoying to the point of I will give up until a fix.

I got this last night while in a section of Osaka harbor. I'd quit and get a message about some Nvidia driver process crashing but recovering. Problem cleared up as soon as I left Osaka harbor.