I've been trying for a few days to get carrier aggregation working on my MR600 v5 and I've run out of ideas, so I'm hoping someone here has solved this or can tell me it's a lost cause.

The router only ever connects on one LTE carrier. It never brings up a second one, so my download is stuck around 25 Mbps whatever I do. What bugs me is that the same SIM, in the same room, does 140-160 Mbps in an old iPhone 6s and over 200 Mbps in my work laptop's built-in modem. Both of those aggregate two carriers, so the cell, the network and the SIM all support it here. Only the MR600 won't use it.

I'm on yesss! (A1 network), Austria.

Here are the actual readings, in case they help someone pin it down.

Radio status from the router (LTE_NET_STATUS OID), both at idle and during a fully saturated download:
- Network type: LTE+ (netType 7)
- Serving cell: EARFCN 2850 (B7)
- PCellValid: 0, SCellValid: 0 (no secondary carrier, ever)
- SCellChannel / SCellBand: 0 / 0
- RSRP: -51 to -63 dBm depending on band, RSRQ: -8 to -9 dB, SNR: mid-20s dB, RSSI: -54 dBm, packet loss: 0%

Throughput through the router (Apple networkQuality, several parallel streams):
- about 25 Mbps down, 33 Mbps up
- download is consistently lower than upload, which for LTE is the wrong way round and makes me think the downlink isn't doing MIMO or aggregation

I locked each band by hand and ran rough download tests. Every combo re-attaches fine on LTE+ and the signal stays excellent, but SCellValid stays 0 in every single case:
- single band: B3, B7, B20
- pairs/sets: B3+B7, B3+B20, B7+B20, B3+B7+B20, B3+B7+B8+B20
The second carrier never attaches, even with B3+B7 forced and RSRP at -51 dBm.

One more thing I noticed: on the default network mode the modem drops from LTE to 3G (WCDMA) under a heavy download and the speed falls apart. Setting the network mode to 4G only stops the 3G drop, but it still doesn't bring aggregation back.

The modem is a Quectel EG06 (Cat6). On paper it does 2CA including B3+B7, B3+B20 and B7+B20, so the combinations my network uses should be supported.

I've seen here that the v1 got a beta firmware with manual 4G+ band selection and aggregation control. I can't find anything like that for the v5.

My questions:
1. Does the v5 do carrier aggregation at all? If it does, what actually makes the second carrier attach? Mine won't, even under full load with a near perfect signal.
2. Is there a v5 beta with band lock or CA control like the v1 one? If not, could TP-Link build one?
3. If the v5 simply can't do it, please say so directly so I can stop chasing it and replace it.

Happy to run more tests or pull logs if that helps.

Model: Archer MR600
Hardware: V5.0
Firmware: 1.5.0 0.9.1 v0001.0 Build 251231 Rel.54154n