Iridium Browser has Google Safe Browsing enabled by default. This means within 5 minutes after start and then periodically approximately every 30 minutes, requests to iridiumbrowser.de (keeps a cache of the GSB data) as well as safebrowsing.googleapis.com (source) are made to update the safe browsing database. You can disable it at any time in the settings by unchecking “Privacy -> Protect you and your device from dangerous sites” (advanced settings) to avoid this request.