I know this is not the best place for this comment, but I can't comment in the "Report a problem" any more. Since the latest software change made on the site couple weeks ago, many audios including this one are not reproduced neither on the question opening, nor by pushing the audio button.
Yes, I agree with you brolga007. It seems we now have "swings and roundabouts" as the new software has improved in some areas, but caused problems in others. The "Report a problem" option no longer allows any additional comment to be made. However, for the discussion page to open in a whole new window is an improvement.
The "j" combines with some consonants to a double consonant, thus *olvasja becomes olvassa. The "j" is hidden in the second "s".
Is it an irregular conjugation? Why not olvasja? Isn't -ja the suffix for third person singular?
It's not an irregular conjugation per se, but rather an exception to the suffix rule, that when you have a siblant (s,z,sz,zs) a following j assimilates to lengthen the siblant (e.g. s + j = ss, sz + j = ssz, etc)
Your question is answered in the Tips & Notes section at the beginning of this unit.