Re doors - the issue is with the ASDO system, either being unreliable or with traincrew who aren't sure how to work it properly, or what procedures to carry out when it does turn unreliable.
Re brakes - the main issue is with a system whereby the units need a static brake test (effectively a driver-supervised self-test) every 26 hours. If it gets to 26 hours since the last time this brake test is carried out then the unit throws up some quite alarming fault messages on the computer system (TCMS) but it doesn't specifically say that what it needs is that this test is carried out, so drivers are sometimes unaware what is required, all they know is that the computer is telling them there's a problem with the brakes. There is no notification to the traincrew when this 26 hour time limit is about to elapse, nor is there any way for them to interrogate how long it has been since the test was last performed. The driver might take over a train unaware that it has been 25 hours 30 minutes since this test was last done. If this time elapsed, the driver is required to interpret the fault messages (which aren't explicit), communicate to the signaller to explain the circumstances, and to TOC control dept. what has happened and confirm what is required. They'd have to explain what is required to the guard too. The test itself takes just under four minutes, during which time the unit must be stationary but also must not undergo any condition which would ordinarily apply the emergency brake (such as any door open/released, DSD/vigilance not being reset, pass-com operated - the full list runs to over a dozen conditions). If the static brake test is successful, the fault alarms should clear and the train should be able to proceed normally. The driver would be required to contact the TOC control and the signaller again, and the guard, before arranging to proceed.
If the test fails, either because it detects an anomaly (however minor) with the braking system or because say something breaks the 'brake loop' while the test is being carried out, the train must then be shut down completely and restarted before another attempt can be made at the static brake test.
The logistics of the unit diagrams are such that every unit should have a static brake test done when it is prepared for service at whichever depot / sidings it is stabled (usually overnight), and that should suffice for the maximum length of its diagram for that day. But clearly this isn't always happening.
There are obviously several ways this situation can be improved - better training, clearer TCMS fault messages that the driver can act decisively on, more robust oversight of procedures on depots, more appreciation of the effect of the chain of effects of one person not doing their job right, even just allow drivers to check the time elapsed since the last brake test was done - this can be checked in real time by someone in an office at a laptop, but not by the driver - the one person who it really matters to and who is at the mercy of the procedure if it is about to run out.