You are using an old version of SLP, read the patches and release notes under the WPSLP changelog in WordPress to see if anything may effect you that has already been patched. I cannot support your version
We are currently on SLP version 4.9.22 with SLP 5. in testing.
You may want to review documentation for settings that can help you .
Before posting questions : Please refer to the posting guidelines.
I do not know what you have for settings currently. See suggestions in documentation