There are two important variables that affect AutoCAD Fields.
FIELDDISPLAY determines whether Fields display the gray background that distinguishes them from other Text. This background is a visual cue only and does not plot. This variable can be 0 (Off) or 1 (On), and is stored in the Registry (i.e. set it once and it is set in all drawings).
FIELDEVAL controls how Fields are updated. This variable is stored in the drawing, and has the following values:
0 - Not updated
1 - Updated on Open
2 - Updated on Save
4 - Updated on Plot
8 - Updated on eTransmit
16 - Updated on Regen
The default value for this variable is 31 which updates on all events, (this is from adding up all the possible event integers: 1+2+4+8+16=31). If you have a drawing with many Fields and it takes a significant amount of time to update, set FIELDEVAL to 15 to turn "off" update on Regen, but still update Fields on all other events. Or you may have a drawing where Fields are not updating as you expect; check the value of FIELDEVAL.
Bonus: Use Lisp to create shortcuts to toggle or set these variables quickly.
; toggle FIELDDISPLAY ON/OFF
(defun c:fd () (setvar "FIELDDISPLAY" (abs (1- (getvar "FIELDDISPLAY")))))
; reset FIELDEVAL to update on all events
(defun c:fe () (setvar "FIELDEVAL" 31))