if you type in "Frank Martin" into person or group control on a form, does it recognize/suggest any user? resp. how many users doe it suggest?
how does it look like a record in history log in step 4?
Taking a cue from your comment, I got what the problem is.
The names mentioned in list are not exactly same as AD names. For e.g. in list it is written as Frank Martin while actual display name in AD is Frank.Martin.
Then I thought to use email address column in list instead of "SomeUser". Now it doesn't show any error but it doesn't pick name either and the "Assigned To" field in workflow is blank as shown in screenshot below.
why not to use 'person or group' field in list directly? it's dedicated for these purposes, and will save you from a lot of problems with conversions.
email address, just like user display name ("Frank Martin" or "Frank.Martin") are not considered to be unique user identifiers.
you can have several Frank Martins with different accounts and different mail addresses.
as well one single person Frank Martin can have several accounts sending to the same mail address.
I'm quite surprised it created a task if it could not resolve assignee, it usually errors out...
if you try the same two tests as I suggested above with mail address, what behaviour do you experience?
I have to read data from this list and it cannot be changed as it is coming from some external system. What I can do is to ask users/system to enter correct name exactly like AD.
ok, I see.
so let's try to figure out what's going on.
reg. mail addressees, have you tried to test this recommendations?
if you try the same two tests as I suggested above with mail address, what behaviour do you experience?
reg. task with no assignee: can you navigate directly to workflow task list and check what value is in 'Assigneed To' column?
did anybody get a task notification?