GLSPs of GJ 3998 ASAS-SN photometry in: (a) Johnson V, (b) Sloan g. Both periodograms are saturated with many peaks. Some of them relate to the stellar rotation period P_rot (solid blue line; circle), the sinusoidal cycle P_cyc in the LTF (solid red line; downward triangle) to 1 yr (solid green line; square). We plot the first few harmonics of each of these signals in dashed lines of a corresponding colour and marker. After this initial filtering, ten significant signals remain: (1) 12.6 d, unidentified; (2) 17.1 d, unidentified; (3) 23.8 d, unidentified; (4) 27.7 d, near the common harmonic of P_rot and 1 yr; (5) 33 d, near the common harmonic of P₇ and 1 yr; (6) 57 d, unidentified; (7) 141 d, unidentified; (8) 233 d, near the common harmonic of P₇ and 1 yr; (9) 276 d, near 2P₇; (10) 393 d, near 3P₇.