I tested the version 2.5.1.11 (see here). Results:
- bluetooth and wifi work at the same time
- wifi has full speed (on 2.4GHz)
- no new errors detected (but only tested for some minutes)
Thanks for helping to solve this issue @irvinewade, @guru, @dos, @Captain_Morgan, @carlosgonz, @Quarnero, @angus.ainslie.