a friend of mine does have an altmonitor issue not updating the relations correctly. in the log we do see a lot of those:

AltMonitor - Manual or per-character entry

what does it mean?

Since AM 2.0, there is an auto-detection mechanism based on character uploads. Relations detected that way are marked, so the guild-based update doesn't overwrite them.
That system detects assuming characters in one upload belong to the same person, and it assigns main status to the highest-ranked character. If there's multiple of in the same highest rank, the highest level counts. After that it's more or less random.
You can turn the system off, but to get rid of the old per-character entries you need to dump the roster_addon_altmonitor table contents, or uninstall/reinstall the mod.

The issue is actually, that the diplay main/alt does not match the ranking in the CharacterProfiler.lua. In fact, the first char with rank 2 ist shown as main, and not the char with rank 1.

I've been thinking a bit about this one. Probably, it's a script error I've fixed since. When I ported AM to 1.8, I also fixed a couple of notice errors. Most of them were in altlist.php, and originated in memberslist.php. Those were fixed in the new memberslist and are now fixed in altlist.
However one of them was in this bit of the update code, and means I've probably been fetching the wrong field for the guild rank check. So it'd only check on level.
Which explains why I didn't run into it as well, because my main has a higher guild rank, and is my only L70.

I'm receiving this message when performing an upload as the GM for my character that I have designated as my main. Is there an issue with Level 0 (GM) that is not being detected?

I'm not sure what issue you're having. If you're seeing the message during upload only, that's normal if character upload detection is on. It also shows up if it ever has been on, since the setting isn't cleared.

I see the message during upload. However, when I click on the Main/Alt button to see the displayed information...all the other players Main's with their perspective alts are sorted correctly.

However my main which is the GM is showing up under one of my Alt's with 2 other Alts and the remaining Alts being classified as Mainless Alt.

Not sure why it is not working for just my characters and is working for the other members.

OK. I'll take a look at it if I've got some time this weekend.

I have been testing out the Alt/Main option within the 2.0 Roster and this issue does not exist. It is grouping my GM main with all the appropriate alts.

So this may be a moot point once we upgrade to the 2.0 Roster

I did look at it a bit last weekend, but I couldn't find anything, and I forgot to post. Sorry.

I seem to remember a past issue in the 1.7.x line when guild masters change. Something with it setting the wrong rank_id. Does anyone know if that issue still exists in 1.7.3?

I believe I am experiencing the same, or at least a similar problem.

Using AltMonitor 2.0.2 with WoWRoster 1.7.3.

When I updated the guild roster initially, everyone was right, alts were allocated correctly with their mains, and all had plus symbols next to the mains.

As each person manually updated their profile, they were allocated as altless mains, and therefore no longer had the plus symbol in front of their names in the roster. Alts, however, were still positioned under them correctly, and indented as expected.

We are using "maintoon's alt" in the player note to define alts, and mains are all those with no result from the regex. ie. We put people's real names in the note for their main, along with their skill. There is nothing to distinguish mains in their note.

No result is set to make them a main. Invalid result is set to make them a mainless alt (the opposite of the problem here).

Update type was set to "Both", but I have since changed it to "Guild" to prevent the problem from occurring every time someone updates their profile.

So I would imagine that there's a bug somewhere in the update process tagging mains as mains without alts if they're updated through the character update page, under the conditions listed above.

Please note: that upon investigation of the roster_addon_altmonitor table, I found the alt_type field of the affected people's to be '5'. I can only imagine that 5 is the mains without alts type, or some kind of error type, without looking through the code. Manually updating these to '0' fixes the problem.

5 is main without alts, per-character update (IIRC). Exact definitions are in altmonitor/conf.php . Per-character updates overrule per-guild updates, and there's no current way to cleanse them.

If you leave it at update on guild only, and delete all entries where alt_type >= 4, it should automatically repopulate them properly after one or two guild updates.