I had the same issue, so I decompiled the game scripts with unrpa. The culprit is basically a badly-coded if block which checks which event to start with Avril (see screenshot). If you've already done the first date event with Megan and the Avril home date (cunnilingus) you've basically locked yourself out of the first practice event. What worked for me (although I'm not yet sure if it will break Megan's events) was using the console to set megan_first_date, avril_licking_pussy, and meet_at_avril_at_home_phone to False, and set first_practice_phone_called to True (which it should already be). After that you can meet Avril in the morning to see the first practice scene - and hopefully progress with Lin's story.
UPDATE: After doing the first practice event, reset megan_first_date to True (otherwise Avril's hint is stuck to "Make thing clear with Megan before other thing"). You then repeat the date event with Gwen, and the cunnilingus event with Avril and proceed normally with the band's second practice.
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