But it is a problem when it's not a deliberate evocation of the character-in-the-moment but rather a lapse in fleshing out the author thought ("He's going to the bank," "She's telling her story") into a scene. A scene is more than just dialogue, more than just movement. Usually a scene has setting, action, dialogue, thought and feeling (from the POV character), or some combination thereof.
Not to say that we can't strip a scene down to a Hemingwayesque quick-fire dialogue without even any tags... but that will be all the more impressive in contrast to more fully fleshed out scenes. And of course, there ought to be a reader-experience reason. It's kind of like walking down the street in your underwear -- that might be a statement, but not if the reason is just "I forgot to finish dressing."
What do you want the reader to get out of this passage or scene? Most scenes probably will have a couple layers at least. At least we will know enough setting to have a sense of inside/outside, day/night; enough POV that we know who the POV character is, or if this is omniscient or objective POV; enough exposition that we are aware that Linda is Joey's mother, not his girlfriend. What does the reader need to know?
There can be no subtext without text. So we need to supply the text. HOWEVER, that doesn't mean the reader needs to be told everything. Here's an example. You might know the play Trifles-- brilliant 1-act kind of proto-feminist by Susan Glaspell. What I found, researching this play, was that Glaspell had later adapted this as a short story, A Jury of Her Peers (note the significantly more "explanatory" title).
I loved the play, even just in text without the actor interpretation and the staging. I was not so blown away by the short story. Why? I think it's because the playscript (which has dialogue and action but no internalization or "POV") gives just enough information, particularly in the actions of the characters, to let the reader figure out what has happened. (It's sort of a little murder mystery-- why did the wife kill the husband? The male sheriff thinks it must be insanity, therefore no trial, because after all, a woman would have to be crazy to kill her husband! But the women in the play find something that explains the motivation, and .... well, read it. It's good.) But the short story explains a bit too much. (Now I don't know if I might have liked it better if I hadn't first read the playscript.)
Anyway, it's hard to get the ingredients in some Goldilocks proportion, not too much, not too little. But I would suggest that most (not all) scenes, if they don't have internalization that reveals the thoughts and/or feelings of the character, then maybe the action should compensate in supplying the additional layer of meaning that could allow for subtext, theme, symbol, all that deep stuff. That would assume that we choose meaningful action, which adds to or contrasts with the dialogue in some way that reveals more or another meaning. Like here from Trifles:
SHERIFF We'll be right out, Mr. Hale.
[Hale goes outside. The Sheriff follows the County Attorney into the other room. Then Mrs. Hale rises, hands tight together, looking intensely at Mrs. Peters, whose eyes make a slow turn, finally meeting Mrs. Hale's. A moment Mrs. Hale holds her, then her own eyes point the way to where the box is concealed. Suddenly Mrs. Peters throws back quilt pieces and tries to put the box in the bag she is wearing. It is too big. She opens box, starts to take bird out, cannot touch it, goes to pieces, stands there helpless. Sound of a knob turning in the other room. Mrs. Hale snatches the box and puts it in the pocket of her big coat. Enter County Attorney and Sheriff.
COUNTY ATTORNEY [Facetiously.] Well, Henry, at least we found out that she was not going to quilt it. She was going to--what is it you call it, ladies?MRS. HALE [Her hand against her pocket.] We call it--knot it, Mr. Henderson.
While the dialogue is all compliance, all women being obedient, the action (hiding the bird is hiding the evidence that would convict Mrs. Wright) shows what's really going on. That's good writing, juxtaposing two conflicting "accounts" really and letting the reader figure out what it means, that the women are protecting another woman from the misunderstanding by the law.
Here is part 1 of Trifles performed by a college troupe. (Part 2 and 3 will be linked on the left.)
Anyway, a scene might be flat if there isn't another element supplying amplication or conflict with whatever is on the surface of the scene (often it's dialogue mostly). If there's a reason you're not in the POV of the character, so you're not showing the thoughts and feelings (and I think there are good reasons occasionally to stay more distant in POV), then consider not just going with dialogue, or an objective narration, but adding in one or two more narrative elements, especially if the action can contrast in some way to add more meaning.