Xiaomi AX3600 5 GHz AX bad performance

using stable OpenWrt 23.05 there seems to be something wrong with the 5Ghz AX performance. Compared to 5 GHz AC, AX connection has lower download speeds and worse latency. Also there are spikes in AX latency. Tried different channels, channel widths, other configurations, latest firmware snapshot... In the attachment are the highest speeds measured for both AC and AX.