Make the runs comparable
Use the same player build and display. Record time to start, number of stalls and whether quality changed. If the wired and wireless runs choose different quality automatically, note that difference rather than comparing only pause counts.
Narrow a wireless-only result
Test nearer the access point before replacing equipment. If it helps, try the usual viewing position again with doors and other devices in their normal state. If the app fails on both links, a second source at the same quality tells you more than another router change.