[SalesForce] Can’t get refreshApex() to work in lwc

I'm not able to get refreshApex() working in an lwc. I've read the docs here — scroll to the bottom. Here are the key elements of the js file:

import { LightningElement, track, api, wire } from 'lwc';
import getBlasts from '@salesforce/apex/Blast.getBlasts';
import { refreshApex } from '@salesforce/apex';

export default class BlastWaveTree extends LightningElement {
    @api recordId;
    @track blastData;
    @track error;
    @wire(getBlasts, { CampaignId: '$recordId' })
        wireBlastData({
            error,
            data
        }) {
            if (data) {
                let tempjson = JSON.parse(JSON.stringify(data).split('waves').join('_children'));
                this.blastData = tempjson;

        } else {
                this.error = error;
        }
    }

    @api
    refresh() {
        return refreshApex(this.blastData); 
    }

My code varies from the doc examples for 2 reasons:

1. The example code doesn't separate out the Apex response into error and data, the pattern I've been following as shown elsewhere.
2. This data is going into a lightning-tree-grid so I have to process it a bit before assigning it to blastData.

I've tried return refreshApex(this.wireBlastData) as well, and that doesn't work.

Ultimately, I want to call the refresh function from the parent component (hence, the @api), but I've simplified it (till I get it working) by calling the refresh function from a button on this same component. I added a console.log line in the refresh() function so I know the button is calling the function. It just doesn't refresh. I'm also watching the apex logs as I push the refresh button, and there's no apex activity.

Here's the template:

<template>
<lightning-card title="Blasts" icon-name="custom:custom3">
    <div slot="actions">
        <lightning-button-group >
            <lightning-button-icon icon-name="utility:refresh"  alternative-text="Refresh" onclick={refresh}></lightning-button-icon>
            <lightning-button label={buttonLabel} onclick={toggleWaves}></lightning-button> 
            <lightning-button label="New Blast" onclick={onNewBlast} variant="Brand"> </lightning-button>
        </lightning-button-group>
    </div>
    <div class="slds-m-around_medium">
        <lightning-tree-grid 
            data={blastData} 
            columns={columns} 
            key-field="id" 
            hide-checkbox-column="true" 
            onrowaction={handleRowAction} >
        </lightning-tree-grid>
    </div>
</lightning-card>

What am I missing?

Here's the error detail from the browser dev tools:

    lds.js:2 Uncaught (in promise) Error: Refresh failed because resolved configuration is not available.
    at Object.e.refresh [as refreshApex] (lds.js:2)
    at l.refresh (blastWaveTree.js:4)
    at callHook (aura_prod.js:24)
    at sa (aura_prod.js:2)
    at aura_prod.js:2
    at _ (aura_prod.js:2)
    at HTMLElement.e (aura_prod.js:2)
    at l (aura_prod.js:2)
    at Un.call.a (aura_prod.js:2)
    at Array.forEach (<anonymous>)
e.refresh   @   lds.js:2
refresh @   blastWaveTree.js:4
callHook    @   aura_prod.js:24
sa  @   aura_prod.js:2
(anonymous) @   aura_prod.js:2
_   @   aura_prod.js:2
e   @   aura_prod.js:2
l   @   aura_prod.js:2
Un.call.a   @   aura_prod.js:2
t   @   aura_prod.js:2
Lt  @   aura_prod.js:2
t.$$lwcEventWrapper$$   @   aura_prod.js:2