Many Gmail users have reported issues with Gmail being overly aggressive with its spam filtering lately, resulting in larger numbers of emails accidentally being sent to the spam folder.
While frustrating, there are steps you can take to whitelist senders and train Gmail to get your email delivered properly.
Tips to get wanted emails out of Gmail’s spam folder:
Open Gmail's spam folder regularly to check for misfiled emails. Mark messages as 'Not Spam' to train filter.
Add missed senders to Google Contacts. Gmail prioritizes messages from Contacts.
Likewise, you may add Contacts within Gmail by opening a message, hovering your mouse over the contact at the top right of your email, then from the window that pops up, clicking “add to contacts”.
Use the 'Never send to spam' button in Gmail filter settings to whitelist domains/senders.
From a desktop, use the ‘Not spam’ option when viewing an email.
Consider using categories/labels to automatically filter senders directly to inbox.
Those steps should ensure emails from that sender bypass Gmail’s spam filters and go straight to your inbox.