Yep, someone chewed up the surface with the last pressure washing and now those low spots are holding moisture. Ask me how I know.....................

@millworkman the wood has never been pressure washed, i know because i installed it myself last fall. you think its mildew too?

The surface is entirely smooth, may not look like it in the photos but it is. thanks

Still looks to be mildew though.

So you want it to have a bright ‘new wood’ look forever right? You will need to sand all of that down to one consistent finish and re seal. Whatever the sealer is that is on the wood has failed in those areas.

Try Wet and Forget to remove the mildew.