It very well could be the connectors. It also may be that the shielding was not cleaned when the connectors (any brand) were installed. I was involved in a sweep project last year. 860 mhz. Lots of QR underground. We found lots of high-end roll-off due to dirty shielding. QR connectors, at least the ones we were using, have a ceramic insert that compresses against the inside of the shielding. This means only the outside of the shielding makes direct contact with the metal of the connector. Poor splicing habits eventually caused major sweep issues. Guys, always clean off the shielding on UG cable before you put on those fittings!
This is CABL.com posting #336577. Tiny Link: cabl.co/mbzIP