This section of the aprs.fi user guide goes through common problems.
If your APRS position is not showing up on the site, the most common problem is incorrect symbol setting in the tracker. Please check the raw packets to see the error messages (enter your callsign and click on Search). If you have a problem with the symbols, please check the APRS symbol configuration page on the APRS Wiki.
You should also check if your positions show up on other sites such as DB0ANF and findu.com. If the positions are not showing up on the other sites, the problem is most likely in your tracker's configuration or the local APRS network (or lack of it). Please get in touch with either another local APRS user, or your tracker's user group. Many of them are listed on the google group's front page.
If the positions are showing up on other sites but not aprs.fi, please check the raw packets again. aprs.fi is sometimes a little bit stricter than others about the packet syntax correctness, especially when it comes to symbol settings, and might reject a broken packet which others digest happily. Sorry about that.
This can happen due to many reasons, including:
The first two are easy to fix. The second two are harder to track down, but their effects can sometimes be mitigated by reducing the transmitting rate and using a shorter path, so that the packets do not go to a faraway broken digipeater.
aprs.fi tries hard to filter old positions, but sometimes they still get through. Because APRS packets do not contain sequence numbers and usually do not contain timestamps, it's hard or impossible to properly catch the duplicates.
There is a long blog post describing issues with duplicate and delayed APRS packets on the aprs.fi blog.
At my workplace, there are sometimes problems with the web proxy server, and the CSS files defining the style and layout fail to load, resulting in a broken layout. This can be cured by doing a "power reload" by pressing CTRL and clicking the reload button (on IE). On Firefox, it's SHIFT-reload, and on Mac Firefox, you need to keep the Apple (Command) key down while clicking the reload button. Alternatively, you can try clearing the browser's cache (temporary files).
If this doesn't help, you're probably running a very old web browser (such as Internet Explorer 6, 7, 8). The old browsers are quite badly broken, and it would take an awful lot of time for me to make the site work with them. New browsers just work.
If you're running a modern browser and still see layout problems (or any other problems), please let me know through the google group.
The map is faster when there are fewer markers visible – just try zooming in a bit. In Preferences => Filtering you can hide some target types you're not interested in. Selecting Show with track instead of Track + waypoints will hide the small red dots indicating transmitted positions along the track, which will reduce the amount of markers and might give a considerable speed-up.
aprs.fi user guide