@Sunshine 

The other router is a ZTE MF281-1.0 modified for Telekom but open to other SIMs. Both routers use B1 and B7 in automatic mode. Same SIM, same location, ZTE keeps both bands stable, TP-Link not. The ZTE router does not have a manual setting for the frequency bands, on the MR600 I would prefer 7 and 28 but it is also not stable.

  @Sunshine 

Thanks for the offer and your efforts, but remote access to my PC, no, I don't want that. This is nothing personal and nothing against TP Link, but my cooperation has its limits. I'm sorry.

  @Ingo_B. the carrier aggregation is working just fine but only engages when required. at idle it stays at one band only. also v3 also worls like this.

  @Sunshine Hello! When is the final version of the firmware expected to be released?

  @redowman In my region (Kazakhstan) frequency bands B1 and B3 are used. On the B3 band, frequency aggregation works like yours. On the B1 band, frequency aggregation does not work! Unfortunately, my Internet works fine on the B1 band. It’s a pity that frequency aggregation does not work on this range. If it is possible to enable frequency aggregation on the B1 band, I am ready to cooperate with the developers. Google Translate.

P.S. Now I checked the frequency aggregation from the phone, it turned out that the frequency ranges B1+B3+B3 are used.
B1+B1 is not in my area. But I noticed that the modem does not work in the B1+B3 range, only B3+B3, and what’s worst is that frequency aggregation only works for sending, it doesn’t work for downloading! This is a beta version of the firmware.

  @redowman  If this statement were correct, carrier aggregation would have to be maintained as long as a download is running or content is being streamed, but that is exactly not what happens.