>>105739685
Could be anything. Maybe it's the only device using the 2.4GHz band while the band being interfered by let's say various Bluetooth devices.
>>105744209
By older you mean few peers? Relying on DHT is a hit or miss and not every peer supports it.
>>105744272
Also this, being firewalled makes up even less connectable peers. Enabling IPv6 could also make you more connectable.