Honestly, when i check the URL "https://dl.google.com/dl/android/maven2/com/android/tools/build/aapt2/8.3.1-10880808/aapt2-8.3.1-10880808.pom", it gives correct response and downloads POM file but could you also please try below setting as defining new Maven repository with custom Google Maven repository?
repositories {
jcenter()
maven { url 'https://maven.google.com' }
google()
}
Normally google() is shortcut for https://dl.google.com/dl/android/maven2/ but it might also worth to try above setting.
Links
All these URLs seem to be correct.