The tmpfiles table that was introduced recently is invalid in Mariadb 10.1.14 (and perhaps in other setups as well).
The "path" field is used as a primary key, but it is too large, resulting in a db error:
WordPress database error: [Index column size too large. The maximum column size is 767 bytes.]
CREATE TABLE wp_h5p_tmpfiles ( path VARCHAR(255) NOT NULL, created_at INT UNSIGNED NOT NULL, PRIMARY KEY (path), KEY created_at (created_at) ) DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci