As of #11466 we no longer have any logic to prevent a user from opening a wallet twice in two instances simultaneously. Not only could this break BDB (without the -privdb=false option, which I have really no idea why we even have a tuneable option for that), but we certainly don't have logic to handle such a case gracefully. It was noted in the original PR's description, but somehow was never followed up on before merge.
{
protected:
    mutable CCriticalSection cs_args;
    std::map<std::string, std::string> mapArgs;
    std::map<std::string, std::vector<std::string>> mapMultiArgs;
public:
    void ParseParameters(int argc, const char*const argv[]);
    void ReadConfigFile(const std::string& confPath);
    /**
     * Return a vector of strings of the given argument
     *
     * @param strArg Argument to get (e.g. "-foo")
     * @return command-line arguments
     */
    std::vector<std::string> GetArgs(const std::string& strArg) const;
    /**
     * Return true if the given argument has been manually set
     *
     * @param strArg Argument to get (e.g. "-foo")
     * @return true if the argument has been set
     */
    bool IsArgSet(const std::string& strArg) const;
    /**
     * Return string argument or default value
     *
     * @param strArg Argument to get (e.g. "-foo")
     * @param strDefault (e.g. "1")
     * @return command-line argument or default value
     */