I’m guessing that you’re just trying to view tiles that haven’t been rendered yet. If you look at the “START TILE” and “END TILE” messages in the log, you’ll see that it might take a few seconds to render a tile. The first time you try and view it there won’t be anything there, but the second time there will be an old tile to view while the new one is being rendered.
If (in an imaginery example)it takes 2 seconds to render each tile then it’ll take 4 seconds to rendering 2 one after the other. It might take longer then 4 seconds to do both at the same time. Normally you’d tune things to render the number of tiles at the same time that your system can cope with.
If you’re using mod_tile / renderd, they’ll probably be in a directory below “/var/lib/mod_tile”. You’ll see one directory per zoom level.
The problem with that approach is that you’ll render lots of tiles for areas that people never want to look at (such as the middle of the sea). Here’s the example disk usage numbers for each tile layer for a server that I look after:
If all tiles in all layers were rendered, you’d expect each layer to use 4 times the disk space of the previous zoom level - even zoom 13 would need vastly more space than it actually does.