We assign anonymous users Visitor IDs of the form "_PENDO_T_ID" (e.g. "_PENDO_T_mvugjpoysuT") when a Visitor ID is not assigned within the Pendo installation snippet. This anonymous ID is generated by Pendo and tracked by a cookie. It is possible for a single visitor to be associated with multiple anonymous IDs because a new ID will be generated if the cookie is not present.
Turn on Anonymous Visitor Data
In order to see anonymous visitor data in Pendo, you will have to check "Show Anonymous Visitor Data" which can be found by clicking your username in the bottom left-hand corner > Site Settings (this can only be accessed by admins of the Pendo subscription). You will also see an option to show guides to anonymous visitors here.
If you did not wish to have anonymous data then you should send the visitor identifiable meta-data through the installation snippet. The installation snippet should be available on all URLs you intend to have Pendo installed on.