Photos and email problems after upgrading to El Capitan

Since upgrading to El Capitan on my iMac about four weeks ago, I have had a couple of issues with Photos. First, for any photos uploaded since the upgrade, I am unable to view them in Full Screen. When I click on Full Screen under the VIEW banner, the photo becomes only marginally larger than it was. Photos that were on the computer prior to the upgrade can be viewed in Full Screen.

More importantly, I’m having horrible issues with mail disappearing and otherwise acting strangely. It seems that items between February, 2015 and Nov. 13, 2015 in my all my individual mailbox folders are gone – not in Trash or All Mail, just gone. In my Inbox, there is a particular problem with items between Oct. 27 and Nov. 6. As well, messages received after that do not appear in “All Mail”. In my “All Mail” folder, every message from certain individuals between Feb and Nov of this year has gone. Monthly reports from a person at my bank are not there from Feb. to Nov. Fortunately I have copies of many of those emails on my iPad so all is not lost.

For the past two weeks, when an item sent by me goes into the Trash folder under Gmail, it appears 6 or 7 times consecutively – same email. This does not happen for messages from others that I put into Trash

Many of my messages end up being in a folder caller “Important”, which folder I did not create. The same is true for my wife’s email.

My wife has a different desktop on this machine and has not had any of these difficulties, except for the “Important Messages” folder. As well, her interface is now slightly different than mine and this was NOT the case before the upgrade.

Very strange. My Default Mail Reader is Thunderbird.

I guess I could use Time Machine to check back to the day the problems of the disappearing emails started, to find the missing emails, but I am not comfortable with that.

Help requested. Thanks.