Is it promoting you to reindex or does it just happen? If the latter, check whatever your are using to start bitcoin core that it doesn't have the -reindex option set.
It just happens. I launch bitcoin-qt from the start menu in Xfce4. The .desktop is as follows:
[Desktop Entry]
Encoding=UTF-8
Name=Bitcoin
Comment=Bitcoin P2P Cryptocurrency
Comment[fr]=Bitcoin, monnaie virtuelle cryptographique pair à pair
Comment[tr]=Bitcoin, eşten eşe kriptografik sanal para birimi
Exec=bitcoin-qt %u
Terminal=false
Type=Application
Icon=bitcoin128
MimeType=x-scheme-handler/bitcoin;
Categories=Office;Finance;