The issue has been resolved. It was not an issue with the feature vector.

It was an issue with the WKT format. I modified the method write in WKT.js as follows.

write: function(features) {
        var collection, geometry, type, data, isCollection;
        if (features.constructor == Array) {
            collection = features;
            isCollection = true;
        } else {
            collection = [features];
            isCollection = false;
        }
        var pieces = [];
        if (isCollection) {
            pieces.push('GEOMETRYCOLLECTION(');
        }
        for (var i=0, len=collection.length; i<len; ++i) {
            if (isCollection && i>0) {
                pieces.push(',');
            }
            geometry = collection[i].geometry;
                        <b>if (!geometry) {
                                geometry = collection[i].feature.geometry;
                        }</b>
            pieces.push(this.extractGeometry(geometry));
        }
        if (isCollection) {
            pieces.push(')');
        }
        return pieces.join('');
    },
        
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