We've had reports of category totals not showing up in Moodle since we upgraded to 1.9.5., much like the issue reported earlier in the forums:
http://moodle.org/mod/forum/discuss.php?d=140426
In most cases the solution suggested there (hiding and unhiding course totals in categories and items) will fix the issues we've been having. We have one gradebook however that has not responded to any attempts to fix it and stubbornly refuses to show category totals.
It is set to weighted mean of grades for all categories and subcategories. There are a handful of items that are not categorized. One category will sometimes show its subtotal and that is the only item being used to calculate the final total. Aggregate only non-empty grades and Aggregate including subcategories are checked for all categories and subcategories. I tried unchecking them as suggested in this forum
http://moodle.org/mod/forum/discuss.php?d=139368
but it made no difference to the report view. I also tried adding all of the uncategorized items to a new category but that didn't work either (neither the new category nor any other category would show its totals). The one category that sometimes works has a grade for each item and no hidden items (some of the other categories have hidden or ungraded items but not all and no other category displays totals). Sometimes it displays a 0 as the total even though there are graded items but all other categories simply display a - as the total.
I've read all the gradebook documentation I can find and searched the forums but haven't found a solution. Is there something obvious I'm missing? Does anyone have suggestions for other things I could try? Thank you very much.
When did you upgrade? On our first test upgrade over a year ago this happened to us so we decided not to upgrade then. I think the issue was fixed since then. For us it turned out to be the aggregation method. As soon as we went into a gradebook and changed the aggregation method to what it was supposed to be the totals appeared. I think it makes a difference as to what you set your default aggregation to during the upgrade so it knows how to aggregate everything. After the fact I don't think it would change anything.
We upgraded from 1.8.6. to 1.9.4 at the beginning of last summer and then from 1.9.4. to 1.9.5 at the end of summer. I don't remember doing anything special with changing default aggregates during the upgrade so I probably did something wrong. I'll try changing the aggregation method in a test instance and see if that does anything. Thanks for the suggestion.
It does seem to have something to do with the aggregation method - category totals will show for simple weighted mean or sum of grades but not for weighted mean.
Found the problem - the instructor had set most of the weights to 0 instead of 1 in categories and items. Thanks so much for the help.
oh... lol. Yeah that'd do it 
My guess is you will probably see this again! Although, I guess that depends on how many courses were fixed since the upgrade last summer. We did the exact same thing. Upgraded last summer from 1.8 to 1.9.4 and had to revert because of this. If you find you are still having issues, the comments in the bug tracker might be of some help: http://tracker.moodle.org/browse/MDL-14059
My guess is you will probably see this again! Although, I guess that depends on how many courses were fixed since the upgrade last summer. We did the exact same thing. Upgraded last summer from 1.8 to 1.9.4 and had to revert because of this. If you find you are still having issues, the comments in the bug tracker might be of some help: http://tracker.moodle.org/browse/MDL-14059
Oh BTW ... my guess is that your problem was most likely due to the upgrade and aggregation method issues because the default behavior when you change aggregation method from Simple to Weighted and Extra Credit is not checked is for the weights to default to zero. Regardless of whether or not weights were in there previously. So if you changed it to test it it might have put zero in when you put it back. Just letting you know as we went through all of this already and I know a lot of the hiccups!