Fixing deprecated code, relatedTo issue
This seems to have fixed the issue.

{% if reldata %}
    {% set tag = craft.tags.title(reldata|join(', ')) %}
    {% set feat = craft.entries.section(data|join(', ')).relatedTo(tag).limit(8).all() %}
{% else %}
    {% set feat = craft.entries.section(data|join(', ')).limit(8).all() %}
{% endif %}