Hello!
About 8 years ago I have set-up a cAPsman on a RB433GL board, and through one switch and three 802.11ac links (SXTsqac or DiscLiteac), total of 8 cAPs. The hardware was mostly old and various (Alix 2d2, Alix3d2, RB433, RB433GL, cAP, cAP lite, mAP and one pwr-over-mains). Devices had one or two wifi cards, but only one was used, usually connected to shot pigtail and 5dBi omni antenna (where applicable). The clients were limited to 20-25Mbps due to 802.11g or n cards, uplink was about 100Mbps link with two LGH xl 5ac, a 25km link. The location was prone to loss of power, from once a month to once a day.
Nevertheless, it worked like a charm for years, but about a month ago people started complaining with one problem. The sentence was almost the same one:" I am connected with excellent signal, but no traffic is going through!" cAPsman would report a client signal of about -50dB, but the speedtest.net would say 0.5Mbps! Stranger still, the Bandwidth test from the network to uplink was at least 100Mbps, always. Furthermore, if the client was connected via ethernet, it got maximum, stable bandwidth of the uplink.
What made us even more confused was that some cAPs worked for some time and then the traffic would slow down, only the restart was helpful. Two worked most of the time (they had additional WiFi links between main location).
We tried exchanging the RB433GL for faster hardware, to no avail. Total number of clients (25-30 clients) in the network was not increased, and traffic was more or less the same. Flashing from 6.49.x to 7.15.1 made no difference also. Four devices could not be flashed (Alix, SXTsqac, cAP, DiscLite ac), reporting that they did not had enough space (but other same hardware flashed without problems).
It took days. To make long story short, after exhaustive testing, we took down all devcies with WiFi cards and tested them outside cAPsman network, as standalone APs. We realized that total of 5 WiFi cards were reporting good signal, but data throughput was painfully slow. So we replaced them all for new devices (cAPs), and now the network works just as before.
Edit: Just two weeks ago I found another location with v6.49.8 that does not use cAPsman, but has same low-bandwidth problem, but on a single x86 router. What is going on with it?