There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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bilingual_str errors;
    for (const auto& arg : args.GetUnsuitableSectionOnlyArgs()) {
        errors += strprintf(_("Config setting for %s only applied on %s network when in [%s] section.") + Untranslated("\n"), arg, network, network);
    }
    if (!errors.empty()) {
        return InitError(errors);
    }
    
    bilingual_str warnings;
    for (const auto& section : args.GetUnrecognizedSections()) {
        warnings += strprintf(Untranslated("%s:%i ") + _("Section [%s] is not recognized.") + Untranslated("\n"), section.m_file, section.m_line, section.m_name);
    }
    if (!warnings.empty()) {
        InitWarning(warnings);
    }
    if (!fs::is_directory(gArgs.GetBlocksDirPath())) {
        return InitError(strprintf(_("Specified blocks directory \"%s\" does not exist."), args.GetArg("-blocksdir", "")));
    }
    
    std::string blockfilterindex_value = args.GetArg("-blockfilterindex", DEFAULT_BLOCKFILTERINDEX);
    if (blockfilterindex_value == "" || blockfilterindex_value == "1") {
        g_enabled_filter_types = AllBlockFilterTypes();
    } else if (blockfilterindex_value != "0") {
        const std::vector<std::string> names = args.GetArgs("-blockfilterindex");
        for (const auto& name : names) {
            BlockFilterType filter_type;
            if (!BlockFilterTypeByName(name, filter_type)) {
                return InitError(strprintf(_("Unknown -blockfilterindex value %s."), name));
            }
            g_enabled_filter_types.insert(filter_type);