Anybody know why two of my graphics cards are suddenly not used?

Help please!
Does anybody out there know why this morning 2 of my 3 graphics cards might suddenly become off limits to Boinc. See below for Log file highlighting this. Not used isn't terribly helpful, and as far as I am aware I haven't changed anything apart from turning off the computer last night and turning it on again this morning. I have turned it off and on again, and all 3 GFX cards appear to be working. What can set them to being "not used"?
Hoping someone out there has some suggestions for where to look
Cheers.

04/05/2020 08:56:01 | | Starting BOINC client version 7.16.5 for windows_x86_64
04/05/2020 08:56:01 | | log flags: file_xfer, sched_ops, task
04/05/2020 08:56:01 | | Libraries: libcurl/7.47.1 OpenSSL/1.0.2s zlib/1.2.8
04/05/2020 08:56:01 | | Data directory: C:\ProgramData\BOINC
04/05/2020 08:56:01 | | Running under account mark
04/05/2020 08:56:02 | | CUDA: NVIDIA GPU 0 (not used): GeForce GTX 960 (driver version 450.12, CUDA version 11.0, compute capability 5.2, 2048MB, 1669MB available, 2412 GFLOPS peak)
04/05/2020 08:56:02 | | CUDA: NVIDIA GPU 1 (not used): GeForce GTX 960 (driver version 450.12, CUDA version 11.0, compute capability 5.2, 2048MB, 1669MB available, 2515 GFLOPS peak)
04/05/2020 08:56:02 | | CUDA: NVIDIA GPU 2: GeForce GTX 960 (driver version 450.12, CUDA version 11.0, compute capability 5.2, 4096MB, 3408MB available, 2566 GFLOPS peak)
04/05/2020 08:56:02 | | OpenCL: NVIDIA GPU 0 (not used): GeForce GTX 960 (driver version 450.12, device version OpenCL 1.2 CUDA, 2048MB, 1669MB available, 2412 GFLOPS peak)
04/05/2020 08:56:02 | | OpenCL: NVIDIA GPU 1 (not used): GeForce GTX 960 (driver version 450.12, device version OpenCL 1.2 CUDA, 2048MB, 1669MB available, 2515 GFLOPS peak)
04/05/2020 08:56:02 | | OpenCL: NVIDIA GPU 2: GeForce GTX 960 (driver version 450.12, device version OpenCL 1.2 CUDA, 4096MB, 3408MB available, 2566 GFLOPS peak)
04/05/2020 08:56:02 | | Windows processor group 0: 12 processors
04/05/2020 08:56:02 | | Host name: Morph5
04/05/2020 08:56:02 | | Processor: 12 GenuineIntel Intel(R) Core(TM) i7-5930K CPU @ 3.50GHz [Family 6 Model 63 Stepping 2]
04/05/2020 08:56:02 | | Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss htt tm pni ssse3 fma cx16 sse4_1 sse4_2 movebe popcnt aes f16c rdrandsyscall nx lm avx avx2 vmx tm2 dca pbe fsgsbase bmi1 smep bmi2
04/05/2020 08:56:02 | | OS: Microsoft Windows 10: Professional x64 Edition, (10.00.19041.00)
04/05/2020 08:56:02 | | Memory: 15.83 GB physical, 19.58 GB virtual

Well I have learnt something!

I checked and my cc_config had today's date and an earlier time on it, and when I looked inside it had a host of options that weren't there yesterday including of course "use_all_gpus" set to 0 which I have reset to 1. Also report_results_immediately was set to 0 which I would normally have set to 1

Perhaps more interesting is how these values all got there and I am guessing it's because I was looking in BOINC / Options / Event Log Options this morning and when I was done I clicked "Defaults" rather than putting them back manually. I didn't quite expect it to give me an entirely new cc_config.xml and reset all the non-log related settings. Hey ho. Live and learn. Thanks to any who looked and thought. Cheers