Just happened to me as well, it was working great till like 20 minutes ago.
2021-07-09 10:03:35 - Bought Assorted Fruits Stamp: x NP in xxxms (Est. Profit: x NP)
2021-07-09 10:03:42 - Bought Plains Aisha Stamp: xxx NP in xxxms (Est. Profit: xxxNP)
2021-07-09 10:03:50 - Bought Archmagus of Roo Stamp: xxxNP in 1744ms (Est. Profit: xxxNP)
2021-07-09 10:04:00 - Bought Purple Grundo Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:08 - Bought Healing Springs Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:17 - Bought Mystery Island Heads xxx: xNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:24 - Bought Petpet Growth Syrup xxx: xNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:32 - Bought Desert Petpet Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:41 - Bought Grimilix Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:51 - Bought Advisor Wessle Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:04:59 - Bought Destruct-O-Match Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:08 - Bought Rainbow Slushie Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:17 - Bought Gallion Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:25 - Bought Gormball Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:34 - Bought Stone Armchair Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:43 - Bought Negg Noodles Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:05:52 - Bought Golden Khamette Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:06:00 - Bought Christmas Kougra Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:06:08 - Bought Commemorative Defenders Stamp #1: xxxNP in 1546ms (Est. Profit: xxxNP)
2021-07-09 10:06:18 - Bought Jerdana Stamp: xxxNP in Xms (Est. Profit: xxxNP)
2021-07-09 10:06:26 - Bought Orange Skeith Stamp: xxxNP in Xms (Est. Profit: xxxNP)
Quick fix: Go to settings > General Settings > UNCHECK Puchase Items Not Found in Items Database