The PER HOST Retired Project List and CREDIT are MISSING Causing NEGATIVE Credits on HOSTS (active and retired).
Retired Projects Do SHOW ONLY for TOTAL HOSTS/POINTS.

This host has -21,363 Credits for THIS WEEK and shows NO RETIRED PROJECTS:
http://boincstats.com/en/stats/-1/host/detail/167212459/projectList
Appears the problem started appearing with the 2016-10-30 STATS according to my Daily Total when 40,348 WERE SUBTRACTED to just this host.

TOTAL CREDITS for ALL my hosts/projects possibly have the correct amount due to the fact it shows a list of RETIRED PROJECTS:
http://boincstats.com/en/stats/-1/user/detail/2355328/projectList

Retired Projects:

Project name	Credit	% of total	World Position	Team position	Country position	 

Beal@Home	4,500.00	0.01	211	4	36	Detailed stats

BMG@Home	2,049.31	0.00	90	6	22	Detailed stats

Constellation	14,043.60	0.03	5,276	30	1,473	Detailed stats

CONVECTOR	53,248.90	0.12	329	8	70	Detailed stats

Correlizer	24,365.90	0.05	669	9	157	Detailed stats

Docking@Home	61,662.09	0.14	8,408	37	1,561	Detailed stats

FiND@Home	8,328.78	0.02	11,665	31	1,788	Detailed stats

FreeHAL	201,038.00	0.45	1,852	39	326	Detailed stats

Gridcoin Finance	85,805.06	0.19	156	6	28	Detailed stats

iGEM@home	4,759.34	0.01	260	8	38	Detailed stats

Malaria Control	5,195.26	0.01	40,224	142	7,185	Detailed stats

Physics	2,408.34	0.01	257	6	50	Detailed stats

Plagiarism@Home	910.47	0.00	106	3	17	Detailed stats

QMC@Home	39,347.60	0.09	11,232	75	2,638	Detailed stats

Rioja Science	17,478.99	0.04	470	8	84	Detailed stats

SIMAP	555,747.56	1.25	1,547	43	380	Detailed stats

SimOne@home	223.67	0.00	327	5	54	Detailed stats

Spatiotemporal Quality of Service	1,435.04	0.00	62	2	20	Detailed stats

Surveill@Home	6,966.72	0.02	211	7	37	Detailed stats

Universe@Home Test	41,891.67	0.09	412	9	69	Detailed stats

Retired projects are not processed for host stats.

Then what IS the cause of the negative host credits on 10/30?

Exactly that. I retired some projects and they were removed from combined host stats. That may cause negative credit.