Peter Vajda's Answer:
Since I don't know you personally, or the entire context of the scenario you describe, I'll begin (as I usually do in coaching situations) with some questions. Sometimes, the answers offer insights into "root causes" of behaviors which, initially, often appear confusing or without plausible explanation.
So: You write, "I have a morale issue that has stemmed from myself being absent from work the past year." Did some flavor of a "morale issue" exist before your absence occurred? If so, are the two related?
You write, "However the staff was able to reach me by phone." During your absence, did you proactively "check in" with your staff members just to get an idea as to how life at the office was unfolding, or to keep some degree of connectivity with your staff, not to "check up" on folks?
You write, "Apparently there is discord among the staff over how much time I have not been in the office." What do you think is the root cause of the discord? For example, it is just your "time away"? Was there any discrepancy between the amount of time you were permitted to be away and time others are/were permitted to be absent (for medical reasons)? Was your situation (being away long-term) common? Was it a surprise to others?
You write, "my direct supervisors have not had an issue with the time being out of the office as I have made up the work primarily on weekends or when actually in office". Do other supervisors allow their employees who are absent to operate according to this same policy? If no, why not?
You write, "My staff is not fully aware of the medical condition that I was diagnosed with." Do you think, feel or believe that had the staff known of your medical condition before and during your absence, the morale issue would be a non-issue?
Your ask, "Should I fully disclose my medical condition to my subordinates?" So what effect do you feel such a disclosure at this point would have on the staff?
And, you ask, " ...and now that I am healthy will time itself bring the morale around with being present in the office? What do you think? Really think? Will it? What does your gut tell you?
If these answers do not provide any (root-cause) insights as to the morale issue, how does the following suggestion sit with you?
Reflect on what would it be like if you met with your staff, individually, and said something to the effect,
" I'm telling myself a story that you're unhappy (frustrated, angry...) with me and I'm not sure if it's just a story I'm making up or if there's some truth to it. So, I want to pass it by you and see want you think. Is that OK with you? (Ask this in a place where you two are alone and provides safety for your direct report.)
If it's OK, continue:
"Thank you, So, I'm feeling that your attitude since I've returned from my absence has changed. I'm thinking it's related to my long absence from the office. And that maybe you're angry, resentful or upset that I was out so long (or I didn't check in often enough with you or...add your own "reasons" here), or that maybe you feel I was given preferential treatment by my supervisor or that you (and others) are not treated the same way. Perhaps there's something else going on. Whatever it is, I'd like to know so we can clear the air and move forward together to clear our working environment and our relationship of the discomfort or uneasiness that seems to exist between us."
That's the story I'm telling myself and I'd appreciate very much hearing what you think."
At this point, listen. Don't defend, justify, rationalize, or excuse or in any way your absence. They're entitled to their feeling in this moment. Just listen. You can ask to restate what you hear to be sure you are hearing what they intended for you to hear, their side, to be sure you both are the same page. But no defending or making them out to be "bad" or "wrong" for their feeling.
Once they state their perspective (or maybe there is no issue and your story really is a "story"), then you need to discuss whatever conflict - real or perceived) arises, conflict that is at the root of their morale issue.
Their issue may be solely personal with you (not work-related), it may be related to what they perceive as unfair treatment of you vs. him/her (i.e. policy), or something else. But once you get the issue out on the table, then the direction forward, for you, will become clear. For example, you may need to apologize for not staying in touch with some people; you (your organization) may need to reconsider your leave/absence policies; you may need to speak directly to some folks about changing their attitudes for the good of the team, etc. But you won't know until you have this dialogue.
I hope this helps and I wish you well in your exploration.