UMTS transfer rate

I do some tests with the UMTSStick and Pandora with RISC OS (actually ROM). Since several months (I’m sure not with 5.18 and 5.19 from april.) after 4MB download the the connection is stable but the transfer rate goes to zero (see picture). The Problem is also on the Beagle.

Also interesting is the following:
First, System completely booted from SDFS. UMTSStick is plugged in, wait until active and “connect”. 1.Attempt “Net not aviable”, 2nd one goes … Transfer rate below 10 kbyte / s.
Second, the same system booted as a clone from the UMTS stick SDCard as SCSIFS. Then “connect” … goes immediately, and the transfer rate is 100kByte / s (The same under Linux.)
Multiple attempts always the same result.

The most problems I have with the Pandora and the old Beagle Rev.C and SDFS is involved. On the Beagle xM and the RPi it works better.
Is the first browser I use Phoenix and then for https Netsurf, the transfer-rate-error does not occur so often.

Edit: It was a hope. The results are very unstable. The error is still present :-(