I didn't find anything for this season, but the Chicago White Sox had the worst record by a team after the All-Star Game in 2024, with a record of 14-50.

Interpreted as:

worst record since all star break this season

	TEAM	REC	SEASON	W%	G	W	L	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	PA	TB	XBH	SH	SF	IBB	GIDP	AVG	OBP	SLG	OPS
1	White Sox	14-50	2024	.219	64	14	50	2,146	194	474	81	4	48	187	139	14	560	27	19	2,313	707	133	4	10	2	38	.221	.272	.329	.601
2	Angels	22-44	2024	.333	66	22	44	2,176	250	481	83	5	64	238	205	43	613	53	16	2,443	766	152	5	14	1	51	.221	.299	.352	.651
3	Nationals	27-38	2024	.415	65	27	38	2,163	258	538	109	8	55	243	176	21	473	97	26	2,384	828	172	12	12	4	49	.249	.310	.383	.693
4	Rockies	27-38	2024	.415	65	27	38	2,168	279	518	109	10	75	270	184	19	690	32	12	2,395	872	194	6	18	8	43	.239	.302	.402	.704
5	Twins	28-38	2024	.424	66	28	38	2,233	276	525	117	8	68	259	194	33	549	19	5	2,482	862	193	5	17	8	38	.235	.304	.386	.690
6	Pirates	28-38	2024	.424	66	28	38	2,224	263	532	104	6	61	254	184	29	620	57	9	2,456	831	171	4	15	5	37	.239	.304	.374	.677
7	Red Sox	28-38	2024	.424	66	28	38	2,276	304	566	136	6	81	294	194	30	640	56	15	2,516	957	223	1	15	12	59	.249	.314	.420	.735
8	Marlins	29-37	2024	.439	66	29	37	2,270	301	587	110	11	72	284	198	25	612	73	16	2,529	935	193	13	23	5	42	.259	.322	.412	.734
9	Blue Jays	29-36	2024	.446	65	29	36	2,213	277	552	119	13	69	266	193	36	519	27	7	2,463	904	201	4	17	13	43	.249	.318	.408	.726
10	Reds	30-35	2024	.462	65	30	35	2,156	267	498	99	9	66	257	198	32	587	73	16	2,409	813	174	6	17	2	34	.231	.303	.377	.680
11	Rangers	32-34	2024	.485	66	32	34	2,235	269	523	89	4	75	255	186	20	539	45	11	2,454	845	168	2	11	6	31	.234	.297	.378	.675
12	Rays	32-34	2024	.485	66	32	34	2,190	228	487	95	12	61	214	182	29	623	83	18	2,415	789	168	2	12	9	24	.222	.289	.360	.650
13	Cardinals	33-33	2024	.500	66	33	33	2,250	274	564	108	10	71	265	199	17	511	35	13	2,485	905	189	3	16	5	47	.251	.314	.402	.716
14	Phillies	33-33	2024	.500	66	33	33	2,263	307	577	129	8	80	294	181	27	566	49	8	2,489	962	217	7	11	7	48	.255	.316	.425	.741
15	Orioles	33-33	2024	.500	66	33	33	2,250	312	553	93	11	86	301	229	23	583	35	10	2,524	926	190	3	19	6	30	.246	.319	.412	.731
16	Athletics	32-32	2024	.500	64	32	32	2,167	253	527	103	7	74	243	186	18	553	45	12	2,392	866	184	6	15	3	45	.243	.306	.400	.706
17	Giants	33-32	2024	.508	65	33	32	2,183	266	502	102	16	81	253	172	21	643	37	8	2,393	879	199	3	14	4	46	.230	.291	.403	.693
18	Guardians	34-32	2024	.515	66	34	32	2,163	254	498	85	7	76	246	179	26	501	69	16	2,391	825	168	8	15	8	37	.230	.295	.381	.676
19	Mariners	33-31	2024	.516	64	33	31	2,127	297	494	99	3	76	280	252	58	612	66	10	2,463	827	178	7	19	7	44	.232	.327	.389	.716
20	Royals	34-31	2024	.523	65	34	31	2,203	293	548	104	11	69	282	172	23	497	54	13	2,429	881	184	10	21	8	38	.249	.307	.400	.707
21	Braves	36-31	2024	.537	67	36	31	2,276	297	559	95	6	104	288	219	23	617	25	7	2,538	978	205	7	13	5	59	.246	.316	.430	.746
22	Cubs	36-28	2024	.563	64	36	28	2,176	321	550	106	13	70	305	219	18	497	65	11	2,437	892	189	8	16	9	34	.253	.324	.410	.734
23	Yankees	36-28	2024	.563	64	36	28	2,181	327	546	104	2	97	313	285	18	540	50	9	2,513	945	203	5	24	19	50	.250	.339	.433	.772
24	Brewers	38-27	2024	.585	65	38	27	2,176	311	520	96	18	78	299	234	14	610	84	18	2,450	886	192	9	17	11	36	.239	.315	.407	.722
25	Astros	38-27	2024	.585	65	38	27	2,228	283	582	102	5	80	261	181	28	507	29	8	2,459	934	187	6	16	17	60	.261	.322	.419	.742