I have that same Beseler timer( audible/auto-repeating). I had to re-solder several connections on the X10 switch to get it working. It is mounted on the PC board and I guess the connections get stressed over time. It was a simple fix for me because I am a Electronic Technician.
You may want to have someone good with a soldering iron open the bottom cover and check those connections.
I believe the difference between several short time exposures Vs 1 total is called the "intermittency effect". It is mentioned in Fred Picker's book. I sometimes have to shorten the total time a bit because it seems darker than what is seen on the test strip and it's series of exposures..